## Propellers and Pitch

## from the

Sailnet Tayana List

The following are messages from the Sailnet Tayana-list covering over 6 years of discussion about engines, engine problems, suitability when installed in heavy boats, and engine/prop combinations. The predominant engine is the Perkins 4-108 with limited discussions about Yanmars.

The problem with engine RPM/boat speed/prop pitch comparisons is that it is mostly anecdotal information. The following factors must be considered:

A) Adding a larger alternator changes the pulley size to one with a lesser diameter. RPM’s will indicate 300 to 600 RPM too high. Most Perkins tachometers are not adjustable for these changes. Therefore a boat with the original Perkins tach and a larger alternator will not have accurate RPM readout.

B) Different brand propellers with the same pitch can give dramatically different performances. Prop brand and model is important. The original Tayana propellers do not compare well to an identically sized Michigan propeller.

C) Boat speed instruments may have a slightly fouled impeller or not be calibrated accurately. Currents can confuse GPS Speed-over-ground readings unless two-way runs are done.

D) Finally, any speed comparison is only a snapshot of the boat’s bottom fouling conditions on any particular day. Only within the first week after a bottom painting can this factor be discounted.

Here, and also in the archive article “Engines (props-performance).doc”, are lots of information on prop pitch versus boat speed. Most of it is confusing when trying to make comparisons among boats of the same type. In order to enhance comparisons, Tayana owners are asked to provide updated or new data by filling in the chart below and then sending it to wstrausbaugh@cox.net.

Boat:

Engine | Transmission & drive ratio | Propeller Pitch & Brand | Instruments calibrated? Y/N Tach & Speed | Bottom Fouling C lean or ? | RPM | Speed

Now, the E-mails:

I was wondering what other owners have found to be the optimal propeller pitch?

I am replacing the propeller on my 1978 T37. It has the Perkins 4-108. The previous owner had the pitch changed and unfortunately the metal must have been bent/heated too much because it has some deep pits in it, up next to the hub. Not a galvanic loss like you would see at the edge of the blades. It looks just like it was bent back and forth , back and forth, until it fatigued. My pitch is currently 8 and seems to be ok when running the boat under power. I don't know what it was before because the stamp on the prop is x'ed out and the new 8 is stamped in.

1950 rpm moved the boat 5.5 to 6 knots, and the max rpm was 2950 (8 knots) according to the GPS. Does that sound about right? By the way, my tach reads 2550 at 1950 rpm and 4000 rpm at 2950! Looks I have some work to do on the tach. Also I don't completely trust the speed because the knot meter was probably reading low and the GPS was probably getting some help from the falling tide. But I'm guessing that the numbers above are in the ballpark for acceptable readings. Correct? Thanks.

Ray Slaninka 1978 Tayana 37 April 1999

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Greg
Just to add to the confusion. Que Tal is a T-37 with a 4108 and a Borg Warner transmission with a 1.91 reduction ratio. Prop is 18" by 9 pitch. It pushes Que Tal at about 6 knots at 3500 rpm. Red line is 4100. The formula used by the two prop shops I contacted when shopping for a replacement (the old prop was cracked) suggested a 16 x 10. When I told them the old one was 18 x 9 they thought that was in the ballpark and that I should stick with it if I liked it. The engine shop recommended against over propping in order to keep the RPM’s down because you don't get the full horsepower out of the engine if you do. Que Tal does rev up to the red line, but I only get a couple of additional tenths of a knot. In fact, I think the engine is most efficient at between 2500 and 3000.

Kent Lewis Tayana 37 April 1999

(According to the Perkins 4-108 manual, the engine has a maximum RPM in displacement pleasure boat installations of 3600 RPM. Max cruise is listed as 3000 RPM – Wayne Strausbaugh, 2005)

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Since I started this thread I've been reading it with great interest. I have to admit that I am a little confused, but I guess the old saying "What ever floats (propels) your boat" may apply here. I've tallied up the responses so far and added a few from marine surveys of other Tayana's:

- Yanmar 3qm30 and came with an 18 rh 13 prop on a 1 1/4 inch:

- With a Volvo MD3B 36HP, I motor easily 6 to 6.5 knots, 1600 to 1800 RPM, with a 3 blade Bronze marked Alco 510V 16 X 12:

- T37 with a 4-108. According to my survey the shaft is 1 1/4" and the Prop is 17RH11, 3 blade. (Switched to Autoprop):

- Que Tal is a T-37 with a 4108 and a Borg Warner transmission with a 1.91 reduction ratio. Prop is 18" by 9 pitch. It pushes Que Tal at about 6 knots at 3500 rpm. Red line is 4100.

- Sparhawk had a 18 x 12 x1 1/4 RH with Yanmar 3QM30

- From Survey of T-37 thanks to Jim Guin in Florida: Perkins 4-108, 17 x 11 RH

- Nautical Weaver has a Perkins 4-108, Borg Warner 1.9:1, and a 18 x 8 x 1 1/4 RH (re pitched from 18 x 10?) Why I'm not sure other than he said it was sluggish.

I have two more questions just to make sure I understand over propping. It means a bigger prop and/or more pitch. Right? And more pitch means you will move the boat further at the same RPM, which translates to more speed at a lower RPM. Right? Which means you may not reach max RPM before you hit hull speed. Right?

Bottom line is I'm not really any closer to deciding on what prop I should get. Except I know I don't what an Autoprop (no offense). Maybe I'll take the advice of Patrick Boulter of Barnacle Boulter's in Little River SC and stop by there on the way up the coast to let him put the boat and prop to the test. Thanks for everyone's input.

Ray Slaninka S/V The Lorna Doone April 1999

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Interesting discussions but I think that transmission drive ratio's are needed as well as engine brands to make comparisons. I have a V-42 with a Perkins 4-108 and a Hurth 150 transmission running a 1.95:1 drive ratio. I have repitched the original, factory prop four times, tried a propeller of a different brand, and finally changed to an Autoprop. What I have learned probably applies to all heavy cruising boats:

The original factory prop was 18X10 and gave a max speed of 6.3 to 6.5 Kts. Cruise speed was 5.8 at around 2000 RPM. I repitched it 3 times from 18X10 to 17 1/2X11 (no change in performance), 17X12 (picked up a few tenths of a knot and lost a bit of "thrust" at low speed), & finally 16X13. The smaller diameter prop is a "speed" prop. That is, it is optimized for speed in calm water. Speed went to 5.8 Kts at 1800 RPM with about 6.3 Kts at 2000. Top speed was 7.6 but the engine would immediately start to increase engine water temp. Seven knots was sustainable at 2300 RPM. Low-end thrust suffered greatly with the small prop. Acceleration was cut in half and the boat had a hard time maintaining speed with any wave action on the bow. Moderate pitching (3 to 5 feet) resulted in 4 knots or less. But the boat cruised well in the ICW. The bottom line here is that a smaller prop with more pitch equals better speed but less thrust. I tried another brand of 3-blade prop (maybe a Michigan?) with a pitch of 16X13 but it had a slightly different shaping of the blades and the engine could hardly pull 2000 RPM. I repitched it to 16X12 and it was satisfactory but never equaled the performance of the Taiwan prop. The Tayana prop had wider and thicker blades.

Then I got an Autoprop. The Autoprop was easy to install on a V-42. It is an 18 1/4-inch prop. I simply dove under the boat, placed it on the shaft and tightened the nut. Speeds are now 6.3 at 1800 and 6.6 at 2000 RPM. The engine only has to produce 75 to 80% of its previous horsepower to achieve RPM and fuel savings are at least 20%. The engine never labors. Max RPM is 3600 when stopped and 2800 at 7 knots. Top speed is 7.8 knots but it still runs warm when exceeding hull speed. Thrust is better than any previous prop I tried as well as acceleration. The boat has stopped in 50 feet from 5 1/2 knots! Head seas are no longer a problem. Any loss of speed from pitching immediately results in the prop repitching and speed being recovered quickly. Lots of thrust is available when needed. But the biggest test was when I took another V-42 in tow and made 5.8 knots at 2300 RPM with only a 5-degree rise in engine temp (on a 95-degree day in warm water!). The Autoprop is both a "speed" prop and a "power" or "high thrust" prop. It is reportedly considerably faster than a MaxProp. It is also expensive. But if an owner thinks that his boat requires a larger engine and would also appreciate a 20% increase in fuel range, this type of prop could prove to be a reasonable and money-saving alternative.

Wayne Strausbaugh V-42 C/C RESTLESS April 1999

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NIKIA is out of the water and we are trying to decide if it is our propeller that is making us go so slow. At 1800 RPM’s our Perkins 4-108 pushes our Tayana 37 at 5 - 5.5 knots at flat calm. We have a 3 blade fixed prop, 16x19 left handed, I believe (does this make sense?). I am curious how fast should a boat such as ours go at 1800 RPM’s? We found out that her fuel consumption shoots up over 1800 RPM’s this is why we stay at that level (where we burn .72 gallon/hr).

What is your experiences?

Alexandra on NIKIA August 1999

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Alexandra,

Most of this is from memory as my documentation is down at the boat, but is close.

The 4-108 redlines at about 4100 RPM and gets to its max horsepower of 50 at about 3600. At 1800 RPM you are getting greatly reduced horsepower. According to the prop shop where I bought my last prop, it is common for people to size their props for a reduced RPM’s because they don't like to listen to the motor screaming, but in doing so they lose a lot of power.

Based on my experience, your prop pitch figure is very high, but maybe it is designed to allow lower RPM’s. On my 4108, the prop calculations indicated a 16x10 prop would allow max RPM’s and therefore max power. The old prop, which needed to be replaced as it was cracked, was 18x9 and worked fine. The prop shop recommended we stay with the 18x9 since it was roughly equivalent to what the calculations indicated and the calculations are only to get you in the ball park and then you have to experiment to find the best prop specs for any given boat. (a heck of a good argument for variable pitch props) Any way, a pitch of 19 seems huge.

FYI, my prop is right handed, but that is determined by the transmission and should not be a factor. I burn about a gallon an hour on my T-37 running at 2700 RPM, which gives me 6.5 - 7 knots, depending on sea state. The motor just sounds and feels right at that speed. However, on a miles per gallon basis you are doing a little better than I am, but I'm getting there faster.

I suggest you call your local prop shop and give them your engine RPM’s, HP, transmission ratio, and shaft size. Most of them will be happy to do the calculations over the phone. There is also a web site that has a prop calculator in it that you can do yourself, but I lost the address. A good search engine will find it for you. Hope this was helpful.

Kent Lewis SV Que Tal T-37 #165 August 1999

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I have a feathering, 3-blade prop on my T37 with a Perkins 4-108. Since I just purchased the boat, I have no comment except the boat is a dog under power. Max 5.5 to 6 knots under power. The reasoning I received is that the feathering props are less efficient under power due to the lack of "cupping" on the individual blades. But the boat goes like h---- under sail. I do not know what brand it is but I can look it up this weekend and let you know.

Andy T Windy Blue September 1999

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Just an incidental comment ..... If your engine is not spinning near the top rpm due to a too large of pitch or diameter, the engine will not be able to develop sufficient horsepower; hence, poor performance and low boat speed. Check with the engine manual for "max" rpm and compare that with your actual "under load" rpm. (A diesel that is not operating near max rpm at full load is subject to extreme cylinder pressure causing premature wear, blown head gaskets, etc.) If there is a great difference, consider a less pitched prop or have it re-worked. :-)

Rich Hampel - still a Tayana (MKII) Wannabe. September 1999

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We have a standard 3 blade (?18x12??), and find it difficult to drive her any higher than 6 to 6.5 under power with our Perkins 4-108.. Under sail, she will quickly accelerate up to 7- 7.5 with our new sails and any sort of a decent breeze.

Harvey Karten September 1999

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Concerning the advice that a diesel should turn near max RPM, I would like to add some reservations to that.

1) RPM range is dictated primarily by the transmission drive ratio. Some boats have 2:1 ratios like the Hurth transmission and others have basically 3:1 ratios. The first will run much lower RPM’s at cruise speeds (1800 to 2200 RPM) while the second is designed for RPM’s about 500 higher at cruise.

2) A boat with a 2:1 transmission ratio should never achieve max RPM or anywhere near it. As an example, I have a V-42 with a Perkins 4-108, a Hurth 150 with 1:95 drive, and an Autoprop. I have had 3 or 4 variations of a regular 3-blade prop prior to the Autoprop and have put almost 6000 hours on my Perkins so have lots of experience motoring (too much...). When the boat is stopped, max RPM with a standard 3-blade is around 2550. Underway at max speed, it is a little more (2650 RPM). I have heard quite a few times that "a boat should turn at least 3000 RPM’s if the prop is right" or "near max RPM". I disagree. Even with a prop pitched too small for my boat which resulted in decreased "thrust" or power in a seaway, max RPM never exceeded 2700 RPM.

3) The Autoprop is computer designed for each boat based on horsepower, transmission drive ratio, hull design, and displacement. Mine does everything it is supposed to do and appears properly sized. It will only turn 2600 RPM at my max speed of 7.8 knots at full power. When the boat is stopped, it will turn 3600 RPM since it uses a much lower pitch when it senses horsepower applied but no water flowing over the prop. These RPM’s reflect pretty close to optimum conditions for this engine/transmission combination and should apply to a T-37 as well.

Wayne Strausbaugh V-42 C/C RESTLESS October 1999

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Wayne,
I must respectively disagree. An engine produces its maximum horsepower at a given RPM (and its max torque at a given, though usually different, RPM). If the engine can't reach that RPM then you will not get maximum power. In order to allow an engine to reach its max RPM, and thus assure it being able to reach its max power, the transmission ratios and the prop must be properly balanced with respect to each other and the engine.

Given that all three (engine, transmission and prop) are important, and given that of the three, the prop is by far the easiest and cheapest to replace, it is usually the one that gets swapped around to try to achieve max RPM.

The mere fact that a boat will reach its theoretical hull speed at a low RPM in most situations does not mean that the prop is properly sized and pitched. In fact, it probably means that it is either too large or too radically pitched which would result in it bogging the engine down at higher RPM’s. The real test is will the engine be able to develop its full HP in severe conditions when it is being asked to punch through big waves and/or high winds.

I have also had mechanics tell me that routinely lugging an engine is harmful. Lugging occurs when it is maxed out under the load it is being ask to carry such that it cannot rev higher. Allowing it to reach its max RPM will assure that it can get to the peak of the power curve.

For those reasons, put me down in the max RPM camp.

Kent S/V Que Tal T-37 October 1999

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Bruce, Kent and Wayne,

Is the max power output at a defined RPM also the most efficient level of operation of the Perkins or Yanmar engines? The other issue that I would find helpful in following this discussion would be and efficiency curve of power utilization to speed through the water with different props, but somehow corrected for transmission. (And with a relatively constant loading of displacement). What is RPM for the max power output of the Perkins 4-108? Is it advisable to run it at that level for all day runs? I would assume that with higher speeds (?closer to "hull speed"?), the energy input required increase non-linearly, due to frictional forces, hull resistance, prop inefficiency at higher RPM’s, etc.

The point about not lugging an engine is something that I have also been taught since I was a boy. But what is that point in RPM relative to load. Is it a measure of how much the engine RPM is retarded in percentage when a given load is imposed on it? How does that relate to the optimal idling speed? On the Perkins, I find that it sets to a smooth idle at about 900 RPM. When in gear, I find that about 1,000 RPM is the point at which the engine doesn't increase vibration but allows me to motor slowly in the anchorage. But what factors should I be attending to?

regards, Harvey October 1999

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Harvey,
You darned scientists make everything so complicated.

I've never actually seen the power curve for a 4108, but the good people an Admiralty Marine told me it peaked at about 3500 RPM. I have no idea if that is the most efficient engine speed in terms of miles per gallon, but I suspect that that a lot of other variables enter in to it. As you mentioned earlier, things like load, how smooth the bottom is, and sea state will effect it. I suspect each of us is going to have to find out by trial and error on own boats. Given all those variables, I'm not sure how valuable a generalized efficiency curve would be, even if one exists.

As for running it all day at the top of the power curve (not max RPM) , that should be no problem, assuming a basically sound engine and drive train. Diesels like to work. The problem is can the crew stand the noise. Sailors want to hear the wind in the rigging, not an engine and these 37s are not exactly sound proofed.

I assume your assumption about the non-linearairity (is that a word?) of energy output is correct.

My seat of the pants approach is to find a speed where both the engine and I feel comfortable. This summer, plowing dead into the wind and waves, the engine and I settled on about 2500 RPM. Coming back two weeks later in a dead calm 2800 seemed about right. In that case fuel efficiency was greater coming back, but we also had the current with us so I don't put too much stock in that fact.

A poor answer to your question. Maybe someone else can do better.

Kent Lewis S/V Que Tal T-37 #165 October 1999

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Agree completely with Wayne (? – I think he means Kent. Nobody has agreed with me yet…! Wayne)

An engine that is lugging will develop over-pressure conditions within the combustion chamber. The minimal damage will be a eventual --- blown head gaskets, spun crankshaft bearings, damaged piston wrist pins .....

Thou shalt not have an engine with excessive combustion chamber pressure ... for very long!

Rx: spin the engine between 80% and 90% of max rated rpm. This has been the engineering "rule-of-thumb" for almost all reciprocating engines for almost 100 years. :-)

Rich Hampel October 1999

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Rich,
I'm not sure we disagree and I'm sorry if my answer was not clear. I did not mean to suggest that you should routinely run at max RPM. The point I was trying to make is that you should be able to run at max power.

If by "spin the engine between 80% and 90% of max rated rpm" you mean that is about as fast as you want to run it for any extended length of time, I would agree. But that is contingent on not lugging it at that speed. By using a prop that will permit the engine to reach it's max RPM, you allow it to easily reach the magic 80 - 90% without lugging. Sizing the prop so it can only get to the lower RPM, even at full throttle, is by definition lugging it with all the bad consequences you describe.

According to the local Perkins repair shop, the max RPM for the 4-108 is 4100. 80-90% of that is 3280 - 3690. Since the peak of the power curve is about 3500, sizing the prop to allow the engine to reach max RPM means you can easily and safely run at it's highest power output without lugging it.

Kent S/V Que Tal October 1999

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Just to through my 2 pennies in I have a Yanmar 38hp motor with a 3 to 1 tranny. Engine max RPM is 3400 cruising RPM is 2800 max RPM is 3150 with the prop I have. The prop is 4 blade not a type error 4 blade 22 X 14 cut down to a 17 X 14. My keel is 6 inches wide. Cruising speed at 2800 is 7.2 at full throttle 3150 I get 8.1. With for blades the ride is very smooth nothing rattles in the boat.. With such a wide keel and the boat weighing 28,000 drag was not a factor.

Willi Robles S/V August Wind October 1999

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Well, we have an interesting discussion going here on engine RPM's and props. But let’s look at some technical data on the Perkins 4-108 rather than have to rely on the local mechanic. From a performance chart for the 4-108:

Max torque 78 lbf. ft. (lbf. ft is how Perkins labels it - foot pounds?) at 2300 RPM.

Torque at other RPM's:

1600 – 71

1800 – 75

2000 – 76

2200 - 77.5

2600 – 77

3000 – 74

3600 – 69

. Notice that the 1800 to 2200 RPM range used by most boats with a 2:1 transmission ratio is within 3 lbf. ft. of maximum torque.

Max RPM in displacement pleasure boat installation: 3600 RPM.

Max cruise RPM: 3000 RPM.

Net shaft horsepower is 47 at 4000 RPM and 45 1/2 at 3600.

The Perkins performance chart and the Perkins advertisement sheet that it came from are now posted on the FTP site as well as in the Tayana-list Archives, Engines (props-performance).doc.

Back to the discussion. I still disagree that "a boat does not have the optimum prop setup if it cannot reach max RPM at full power". I have never seen an engine with a fixed 3-bladed prop that would even come close to 3600 RPM with a 2:1 transmission ratio. Not that I have seen that many, but I really have asked this specific question of owners of boats of various kinds. Note the response from Willi Robles. He gets 3150 RPM out of the 3400 max RPM allowed on his engine with a 3:1 transmission. This is pretty much what I would expect from that transmission ratio. I do believe that if a V-42 or T-37 can cruise between 1800 and 2100 RPM and get 6.5 Kts that this is pretty much "as good as gets". This would mean 7 to 7 1/2 KTs at full power (2600 to 2800 RPM's) although I would expect increased engine temps when trying to sustain over 7 Kts. Sure it would be nice to have a prop that would allow the engine to rev throughout the complete power range of the engine. But unless you have an Autoprop, I don't think that this is realistically achievable. The compromise is the prop/ engine/ transmission setup selected by the engineers at Tayana. For those who want to run in the higher RPM range, a 3:1 transmission and matching prop should fill the bill. But let’s collect some more data... If anyone with a 2:1 transmission ratio can achieve anywhere close to 3600 RPM with their engine, please give us the details and your opinion of whether your boat is optimized as far as the prop goes.

Wayne Strausbaugh V-42 C/C RESTLESS October 1999

The following three messages were the only ones received in prior years that directly concerned this subject:

Sirena Originally had a 18x12 prop and I was unable to get much above 2200RPM but was able to go 7.5 knots. Yanmar said, "You sail-boaters are always afraid to burn fuel, that engine should be run at 24-2600 rpm with a max RPM of 2800. You will carbon it up and never reach its proper torque HP range. Your prop has to have some pitch taken out...."

So....I had the prop re-pitched to 18x11.25, can now do 24-2600rpm, but can't get above 6 knots.....So there you have it from me.....Anyone have a 18x12 prop for sale...............

Charles N. T-37 May 2003

Last year we had some discussion on engines overheating and prop pitch. I had the pitch on mine changed (wish I could remember what it was before) to 16 x 10 (3-blade). It immediately increased my cruising RPM’s from about 1800 to about 2500 without overheating. Boat speed increased slightly. – I get between 6 and 7 knots at 2500 RPM depending on conditions.

I would definitely recommend re-pitching as it gets the engine running closer to optimum where you get more of the horsepower out of it. (though I'm still a long way from the 3500 to 4000 RPM’s for peak horsepower of a Perkins 4-108)

Mark S/V Windbird Tayana V-42 cc September 2003

We have a V-42 also but with the 55HP turbo Yanmar, 2.62 gear ratio and 18' three blade max prop. The first year I had the Max prop I had to estimate the pitch (can only really adjust the pitch when the boat is out of water) and the engine at 2,500 or so pushed her to about 6.8 Kts. However when fully opened, I could only get 3300 rpm whereas before with the fixed 3 blade we could see red line of 3500-3600 rpm.

Next year changed Max Prop to next pitch adjust lower (less pitch) and could get 3550 rpm but at 2500 or so the boat is only 6.4knts and the engine feels like it has very little load. To get the same boat speed I need to run 2700+.

# David Laber S/V Hegira V42 April 2001

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I have spent 5 or 6 summers in Maine, dodged well over a million lobster traps, and never picked one up. I have Spurs but believe they have never had to cut anything. My first line of defense is a piece of SS angle iron from the keel to the skeg. I've used it for 6 years without a problem (around 14 to 15,000 NM of cruising). The front of the SS angle iron is attached with large bolts about 6 inches up from the bottom of the keel and below the keel zincs. The keel is solid fiberglass there. This is to keep stress off the bar if I were to go aground while giving me the ability to rotate the boat in mud, etc. The rear is attached to the underside of the bronze shoe on the skeg with much smaller hex head bolts. The idea is that if it comes loose, I want the back end to go first. The angle-iron configuration is very strong and the "L" shape keeps the bolt heads from snagging on anything. It had no apparent affect on the speed of the boat. This configuration should work well on nets as well. I ran over a small log once and it just bounced underneath. See ftp://tognews.com/V-42_Keel-Skeg_SS_Lobster_Pot_Guard.

Wayne Strausbaugh V-42 C/C RESTLESS February 2000

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Having the correct pitch allows the engine cylinder pressure to be a minimum relative value for the horsepower developed. For instance (as extreme examples), if too low a pitch: lower rpm developed; hence lower horsepower .... and extremely high cylinder pressure ('lugging' ) , blown head gaskets, bent piston connecting rods, hammered mainshaft bearings, excessive engine wear, etc. If too high a pitch: cavitating/eroding prop , scored cylinder walls, 'hammered' injectors and valve seats, excessive engine wear.

Most 'steady state' reciprocating engines 'like' to be run (long term) at near 75% of max developed horsepower and at the 75% peak of their 'power curve'. I like to select pitch so that I get 75% optimum rpm/horsepower output at the rated hull speed of the boat. Ever since Drs. Otto and Diesel invented their engines, the value for long life vs. maximum output has been around 75% rpm/horsepower output. Look at the power curve 'optimum' value in your engine manual, match/record/correct that value near the hull speed of the boat and you optimize the whole system for economy, reliability, long life, and extra power 'bursts' when you need it. For me its like religion, politics, taking risks, etc.;... I like to be in the 'middle'.

The Autoprop tends to automatically adjust for the 'optimum' all along the engine power curve. (I just think they are outrageously expensive, as I can almost do a whole engine rebuild for the price of an Autoprop.)

Rich Hampel March 2000

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The factory told me that if the pitch did not allow close to full rpm, it was overloading the engine which could have negative implications over time. Did I read your comment right? Is there a
difference in these two approaches?

David / Hegira March 2000

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Yes, you have it right......... ! If you were underpitched, you would never reach full rpm.

Rich Hampel T-37 March 2000

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A friend of mine with a 1996 V-42 has been concerned about speed under power. Only a little over 6 knots at full power. He had the prop cupped last week and now can make 7 knots but is concerned that he can only turn 3200 RPM. He used to get 3600. The engine is a Yanmar 4J82E (non-turbo) with a KBW 20 transmission (2.17 drive ratio). Anybody with a V-42 have that engine/transmission setup? What kinds of speed-versus-RPM do you get? Anybody have an Autoprop with that Yanmar? Would appreciate any comments that I can pass on.

Wayne V-42 (but with a Perkins) May 2000

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Had the hull cleaned the morning we left Long Island Sound ahead of the Storm on the way back upstate. The diver did a great job as indicated by the clean hull and prop when we took her out of the water last Tuesday. I took the heat exchanger off as well as those items already mentioned and found it surprisingly nice and clean, though I did pass a brass gun cleaning brush through all the tubes. I will be checking the impellers this weekend just to see if a fin broke off or something. I even had the prop re-pitched from the normal 18 x 12.5 to 18 x about 11. I was able to get max rpm under load after having that done, but still had some high temp alarms at 2400rpm. I thought it might also be my water heater. The 3Qm doesn't have a thermostat bypass so the heater was connected from the drain valve of the heat exchanger through the water heater and then tee between the output side of the engine and input of the thermostat. I also put in a bleeder valve in the heater line at the high point of the return hose. The water is warm but not HOT even after a 6-8 hour run...... I'll be awake again tonight.

Charles N. T-37 May 2000

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Wayne,

We have a V42 also but with the 55HP turbo Yanmar, 2.62 gear ratio and 18' three blade max prop. The first year I had the Max prop I had to estimate the pitch (can only really adjust the pitch when the boat is out of water) and the engine at 2,500 or so pushed her to about 6.8 Kts. However when fully opened, I could only get 3300 rpm whereas before with the fixed 3 blade we could see red line of 3500-3600 rpm.

Next year changed Max Prop to next pitch adjust lower (less pitch) and could get 3550 rpm but at 2500 or so the boat is only 6.4knts and the engine feels like it has very little load. To get the same boat speed I need to run 2700+.

We are about to go on a long cruise of 3000 miles or more and I was thinking about changing back to the original pitch to get more speed at an efficient rpm that the engine feels comfortable at and uses less fuel. The guys at PYI (MaxProp) think this is good idea. Do you or any other readers of this list have experience or thoughts on this subject?

While I'm on the prop and related subject, anyone have opinion about SPURS or another type of line cutter for the V42? Are they useful on the V42 as our shaft comes out of the keel and has no prop skeg or exposed shaft to speak of for lines to encircle?

David Laber S/V Hegira V42 April 2001

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Subject: RPM accuracy

There may be yet another thing worth checking if it is fine at "lower RPM" but not at higher. Are you sure about the accuracy of your Tachometer? If you changed the alternator, it may not have the same pulley diameter as the original alternator. The Tachometer on the Perkins Diesel operates off the alternator. After replacing our alternator, I noticed that the engine seemed much more efficient. I now would find that our speed was much higher at a lower RPM. Or so I thought!

I borrowed a flash gun tachometer. It measures the true RPM of the engine by placing a small piece of reflective tape on the main pulley of the drive shaft, and a flash gun, linked to a VOM used to measure true RPM. I discovered that our engine was actually running a full 20% higher RPM’s than indicated on our tachometer. Thus, rather than the reading of 2,000, it was actually going at 2,400 RPM. 3,000 was actually 3,600 RPM. This may contribute to overheating. What prop are you running?

regards, Harvey April 2001

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Harvey,
You certainly touched on a good point when you mentioned tach accuracy. Anytime an alternator is replaced, there is a good possibility that the new pulley is a slightly different diameter. This really plays havoc with accurate RPM readings on a Perkins. I used a mechanical tach right off the crankshaft pulley to calibrate mine. I also had to replace the original Perkins-supplied tachometer since it had no provision for calibration.

The cruising RPM for your Perkins is strictly dependent on your transmission ratio. In general, 2:1 ratio's seem to run best between 1800 to 2200 RPM with a properly sized prop. That RPM range will increase with a 3:1 ratio. Also, the prop size and pitch will usually be quite different with a 3:1 ratio. One of the more common discussions I've heard while cruising, is the happy hour, marina comparison of prop size/ pitch/ engine-to-cruising speed and RPM. I remember hearing that "the engine must be able to reach 3000 RPM underway" and/or "the engine must be able to reach max RPM underway or the prop is pitched wrong". I have repitched the prop 3 or 4 times and changed props 2 or 3 times trying to make that happen. I have had my boat "overpropped" and "under-propped". I finally figured out from a mechanic that Tayana got it pretty close from the factory and that my Perkins is specifically designed and rated for the 2:1 transmission that it came with. I use 1800 to 2200 RPM as a good trade off for speed versus reasonable fuel efficiency.

The performance chart that I posted is only accurate for a Perkins 4-108 with a Hurth transmission running slightly less than the 2:1 ratio. That is why you can see the engine developing max torque in the 2000 to 2600 RPM range. That also explains the 3000-RPM max cruise RPM. A Perkins with a 3:1 transmission ratio may have an entirely different torque curve and RPM restrictions.

Wayne V-42 C/C RESTLESS April 2001

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It doesn't sound like a problem with the prop to me. I have a 50-horse Perkins, a BW Velvet drive 1.9:1 and an 18x8 prop and I can do 3000 in gear. Although maybe your prop is out of spec. Have it reconditioned.

Ray 2001

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You’re getting much better performance (rpm) than I do. I’ve been messing around with repitching the prop (can't remember if the current one is 18x11 or 17x12 or if it's one and needs to be the other). I can't get more than 2,000 rpm...but I’m working on it.

Bill T-37 2001

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Check the FTP site for some info I put up regarding the Autoprop. It is a fairly complete discussion of props vs. speed (links updated August 2005):

ftp://tognews.com/Perkins_4-108_PerformanceSpecs

I have never (in 20 years) been able to run my Perkins over about 2400 to 2500 RPM without a slow rise in temperature. With a Hurth transmission and about a 1:1.95 drive ratio, the Perkins is a little overloaded at high RPM's. That seems acceptable to me in order to cruise with reasonably low RPM’s and long engine life. I would be interested to find out if there is anyone out there that has been able to run at full engine RPM for even 15 minutes without a temp rise. And if so, at what speeds, etc.? I consider the high RPM regime on my Perkins as a temporary, short-term condition for accelerating, doc king maneuvers, etc.

Wayne V-42 C/C RESTLESS June 2002

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Hi Bill & Doug,

With my Perkins 4-108, I cruise at 1800 to 2000 RPM. Never more than 2200 RPM, even when in a hurry. At near 7 knots under power, the V-42 starts to bury her stern and raise the bow. She will sail at or above these speeds easily but will not motor at over 6.5 to 6.8 knots without requiring exponentially greater power settings. I can't see pushing a hull much above its hull speed. The 33-foot waterline length is the limiting factor.

My max RPM underway is around 2600 with the Autoprop and was maybe 2700 with a regular 3-blade. I know that many mechanics recommend that an engine be able to turn 3000 RPM. That may be fine with a 3:1 transmission ratio but it is not feasible with a Hurth running a little less than 2:1 ratio. I even asked the "list" once if anyone had a boat with this engine/transmission combination that would run 3000 RPM and got no positive responses. For your info, all my test data was logged immediately after a haulout (clean bottom), with a calibrated tachometer, and using GPS SOG as a cross-check for the speed log.

Wayne V-42 C/C RESTLESS June 2002

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Sirena Originally had a 18x12 prop and I was unable to get much above 2200RPM but was able to go 7.5 knots. Yanmar said, "You sail-boaters are always afraid to burn fuel, that engine should be run at 24-2600 rpm with a max RPM of 2800. You will carbon it up and never reach it's proper torque HP range. Your prop has to have some pitch taken out...."

So....I had the prop re-pitched to 18x11.25, can now do 24-2600rpm, but can't get above 6 knots.....So there you have it from me.....Anyone have a 18x12 prop for sale...............

Charles N. T-37 May 2003

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My boat had the non-standard taper on the original shaft as well. I changed it when I got a new shaft, then had the hub of the Taiwan prop rebored to fit the standard taper. The standard U.S. taper makes it easier to fit a spare prop if something goes wrong. I don't have a clue what the non-standard "standard" was....

Wayne V-42 C/C RESTLESS August 2003

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Prior to having the prop re-pitched, I was only able to get 2250 RPM under load and max no-load 2500. After the prop was reworked, I was hitting 25-2650 under load and could do just over 3k no load. HOWEVER...as I mentioned in an earlier post, my SOG went from 7 to 6 Kts.....And you know that extra knot is a must especially going through Hell Gate against the currents..ha-ha

Charles N. T-37 September 2003

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Tad,
Last year we had some discussion on engines overheating and prop pitch. I had the pitch on mine changed (wish I could remember what it was before) to 16 x 10 (3-blade). It immediately increased my cruising RPM’s from about 1800 to about 2500 without overheating. Boat speed increased slightly. I get between 6 and 7 knots at 2500 RPM depending on conditions.

I would definitely recommend re-pitching as it gets the engine running closer to optimum where you get more of the horsepower out of it. (though I'm still a long way from the 3500 to 4000 RPM’s for peak horsepower of a Perkins 4-108).

Mark S/V Windbird Tayana V-42 cc September 2003

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This is a repeat of a frequent discussion regarding prop size, engine RPM, max power and max speed.

With all the different experiments by Tayana owners, has anyone gotten the RPM of a Perkins up to 3,000 on a Tayana 37, and how did that affect the boat speed, engine temp, etc. I can understand the concern about running the engine at prolonged slow speed of 1,000 rpm and never higher, but if the engine is at 2,000 to 2,200 rpm and pushing the boat at 6.5 knots in flat water, that seems like decent performance. I also enjoy lolling about in gentle anchorages and up remote fjords at slow speeds. This often means rpm ranges of about 1,000 under minimal load (no major seas, no big currents).

According to the graphs of the Perkins 4-108 on the Tayana ftp site, the torque maximizes at 1,900 - 2,400 rpm. The max recommended cruising speed is 3,000 rpm. Although horsepower does continue to increase at higher and higher rpm, I had always been told that the ideal range of rpm of a diesel engine was in its maximum torque zone. That should also provide a high enough rpm to help blow off excess carbon, etc.

I also was under the impression that fuel efficiency drops sharply when you push above about 2,000 rpm with a reasonably correct prop. Pushing the hull from 5.5 knots to 7 knots can almost double your fuel consumption of a displacement semifull keel hull. At 5.5 to 6 knots, we get about 0.6 to 0.7 gallons per hour, depending upon sea conditions.

I have occasionally pushed to about 3,000 rpm, and got up to 7 knots, but the noise, vibration (even with a balanced engine and shaft), and fuel consumption bothered me.

In contrast, I have run a Yanmar on a Hunter 356 at 3,000 for hours, yet only managed about 6.5 knots, but with a two bladed prop. A recent trip on a 39-foot displacement double ender, similar in many specs to the Tayana 37, running at 2,000 rpm on a big Cummins diesel, gave about 6.5 knots with a fuel consumption of more than one gallon an hour.

According to the surveyor (who was a real turkey), we have an 18x12 prop. Clean bottom, clean prop.

Harvey J. Karten, M.D T-37 September 2003

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I think my prop is not correct; I can only get up to 1700RPM. A diesel mechanic told me that I was probably overpropped. I've searched the archives to "propeller pitch" and found no comments that specified pitch, although I remember seeing them in the past.

I've got a Yanmar 3QM30. Help?

Dean October 2004

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Dean,
No idea if this will help, but we have a T37 w/ a 3QM30F and a Kanzaki-Hurth transmission. We just got a new 17" x 9.5" pitch Campbell Sailor prop (www.westbynorth.com). We're only getting 2100 RPM (should be max 2800). The manufacturer recommends that we send it back and get it repitched to 8".

Mark Kaynor T-37 October 2004

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Hi Dean...

My Prudence has a Perkins 4.108, with a 17 RH 10 prop. I "cruise" at hull speed at the 1500-1800 range, and rarely go over 2000.

John Kalpus Prudence San Diego T-37 October 2004

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I took a diesel mechanics course at Orange Coast College in Newport Beach a few years ago. The instructor was a guy named Terry Brown who was a local diesel mechanic. I learned a lot from him and think I have avoided unnecessary wear and tear on a couple of boat engines due to what I learned from Terry.

Terry told us that you should be able to run your engine up to its full rated RPM in the slip. If not the boat is over propped.

He also told us that the unchallenged leader in causes for diesel engine failures on sailboats is due to the use of inappropriate plastic vented loops on the raw water line just before it gets injected into the exhaust system. The tiny holes in the black Marelon vented loops get filled with salt and become plugged. When that happens the loops don’t vent and a cooling engine can pull water through the raw water pump and fill the cylinders with sea water. Onan makes a bronze vented loop with a flap valve the size of a quarter that eliminates the problem.

John Lewis October 2004

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John,

That seems a bit slow for the Perkins. Does your engine get up to temp (~180). My Perkins will not get to temp until 2800. My Mechanic told me the same thing that was told to John Lewis about max RPM at the dock (actually he said almost MAX RPM, you should be able to hit max RPM while under way. At the dock you are a bit slower since you are getting more resistance from the non-moving water). The MAX RPM for the Perkins is 4000 RPM, so 3600-3800 RPM is about right.

My prop, I think, is a 16" x 17 Right Hand. At 3000 RPM I use almost exactly 1 gal/hr and cruise at about 6.5 knots using a Perkins 4.108.

Regards, Andy T-37 October 2004

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My Perkins doesn't go much above about 2500 RPM, but that may be limited by the pedestal guard, as I can't push the throttle any further, and will have to disassemble it to see if the throttle can be raised further.

If I recall correctly, our prop is an 18x12 3-bladed fixed. We can cruise all day at 2,000 RPM at about 6.5 knots, depending upon wind/waves/current. Our fuel consumption is about 0.6-0.7 gallons per hour. Our overall average is about 10 nautical miles per gallon. Temp hardly ever goes about 170-175 F.

regards, Harvey T-37 October 2004

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I think that I am under propped. I can run at 3000 and above (according to the tach) easily, I usually cruise at 2800, which corresponds to about 6 knots (per the GPS). I intend to measure my prop next haul out.

Speaking about temperature, my Perkins usually runs just under 180 F. On a recent trip to Ensenada, the temp gradually rose to above 200 F. Not too long after this the engine quit due to a clogged fuel filter. After I changed the filter and got the engine going again, the temp ran consistently at the old 180 F value. I am thinking that a fuel starved diesel must run hotter than usual.

Dan Baker T-37 Che Bella October 2004

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Sea Schell has an 18 X 11 3 blade fixed with a 1981 Yanmar 3QM30 that moves her @ 5.5 - 6 knots in flat water.

Harry & Melinda Schell T-37 Sea Schell May 2005

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When I first got Southern Cross, she had a 17x12 prop, driven by a Yanmar 4JHE. This was definitely too small, but probably the original. At 2600rpm, I got about 5.6kts. The engine would also easily exceed max rpm. I now have an Autoprop, 470-H5 (18.5 inches) and at the same rpm, I get about 6.5kts and it won't over rev anymore.

Paul s/v Southern Cross V-42-cc May 2005

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We have an 18" Max Prop on Magic Dragon. When we bought the boat, the previous owner had decided it was under-propped and had adjusted the pitch up a notch, so we were unable to make more than 3000 RPM with the Yanmar 4JHE. The stern would squat severely and black smoke would boil out of the exhaust at that engine speed.

I repitched the prop back down last year and the engine seems much happier. I don't remember exactly what the exact pitch measurements were/are. They're in my logbook on the boat. I'll look this weekend and report back.

If you are thinking of replacing the prop, I would definitely recommend ponying up the extra $$ and going with the Max Prop or Autoprop. More speed under sail, and greatly improved backing ability.

Frank Timmons V42 Magic Dragon May 2005

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EVOLUTION, Hull # 105 has a 17 X10 RH prop turned by a 4JHE Yanmar. With a clean bottom, she will make 5 knots @2000 RPM, 6+ knots @2500. We usually run at about 2800 and make close to 7 knots.

Dick Miller EVOLUTION V-42 Hull #105 May 2005

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Try Baumann propeller service co., 713 926-6908, 2309 Macario Garcia Dr. in Houston. He will need to know info about your boat, weight, engine etc. I bought a new prop for Malachite from them and liked their service.

Dan May 2005