Clutch slip - prop pitch

[POG]

I have had reason to suspect that my Paragon clutch was slipping as I had to crack the engine to at least 2,200 revs to do a measly 5 knots.

With the help of this wonderful community and a previous long member exchange on the subject I managed to tighten my clutch and also, thanks to a comment by the very mechanical RayNWanda, purchased a handheld laser tachometer for just over $14 on the internet.

I attached a small strip of reflective tape (included with the meter) to the forward side of the extra pulley at the engine front, one to the fat sleeve link between the gear box and the V drive and the last one on the prop shaft itself.  This wonderful little instrument now told me that my rev counter on the instrument panel is showing the correct revs.  That I have zero slippage through the gear box and that the V drive does indeed gear the turns down to half of what comes out of the engine and the 1:1 Paragon box.

Any continued slow travel will have to be attributed to the prop, which is old and a bit scuffed and the standard LH 17x12 3 bladed that most of us seem to have.

I am soon to haul and I am strongly inclined to pitch up to 17x13.  A big engine, like the 4-108 I have, should be able to turn that.  In any case, I view the motor as there for almost exclusively no wind / flat seas conditions.

One concern is the added thrust on the V-drive.  Any thoughts?

Carl / POG

[RayNWanda]

 I'm working on memory here, which is suspect. Seems like the standard 3 blade is a 17X10LH, the 2 blade is a 17X11LH. I did a search to confirm that, but came up blank.
Sounds like you have done a good job of verifying that you have no slippage in the transmission. I think you have described your prop as "scuffed" before. What do you mean by that? Anything that changes the profile of the prop is likely to degrade it's performance.
The W-40 is physically a big, heavy engine to be rated at 37 hp, but 37 hp it is. The prop is sized to absorb that 37 hp when the engine is at rated speed. increasing the pitch will be OK at low power settings, because prop power demand drops faster than engine torque as rpm comes down. The problem will come at full throttle when you are trying to enter a pass against a heavy tidal flow, or powering into big seas. That extra inch of pitch is going to drive up combustion temperatures in the engine. Could cause it to overheat, will probably shorten exhaust valve life, it won't help the pistons and rings. It will burn more fuel. More fuel is where the additional heat is coming from. If the bottom is clean and there is no slippage, we are now at the prop. You might take it by a reputable prop shop and have them check it. One thing you don't know is what has been done to it in the past. It may be stamped one thing, but be another. It could also be bent, but not enough to be obvious. If it is the correct pitch and diameter, ask them if it needs a rework. If the prop is right, you should get about 5kts at 2,000 rpm.
Somebody chime in with the correct prop sizes!

[Jim S]

The original two blade prop was 18".  I don't know the pitch, but 11" seems correct.

[EdHouston]

Where are you locted POG I have a buddy who had his prop faired and repaired here at a shop in Houston for a little over $200.00 it looked better than new when they were done with it, I think I agree with Ray stay with the prop as sized better a devil you know than one you dont.

[Dale Tanski]

Garner is the go to guy on this one.  According to the Sea Dragon web site, the two props that came standard on the boat were 18L x 10 2 blade and a 17L x 11 3 blade.

Dale

[POG]

Thanks for the input.  I am in Marin County north of San Francisco, Ed - but we have prop shops here too that refurbish worn screws (I hope you know that that is sailorese for propeller!).

I am hauling very soon and will take the opportunity to have my prop checked and worked at.  The edges of the blades are a bit jagged.  It is certainly not a pristine piece of equipment.

Manuals on my boat suggest that the Pearson prop recommendation for the W40 with the 2:1 reduction V drive was 18x10 LH and to increase the pitch by 2" for every inch of decrease in diameter.

Carl / POG

[RayNWanda]

 The rough edges can be a bigger problem than you would think. Are the rough edges on the leading or trailing edges? I have a prop here that I intend to have reworked for a spare that has cavitation erosion (heavy pitting) on the trailing edges. It appears to be in pretty good shape other than that. At this point, it should be a relatively inexpensive repair. Once that erosion gets started, it does affect the way that water leaves the trailing edge of the blade. It induces turbulence and more cavitation, which eats the trailing edge faster and faster. Dings on the leading edge can cause cavitation across the entire blade. Prop efficiency usually drops quickly, and running it for a long time can cause cavitation erosion across the entire blade, which leads to balance problems. Best efficiency is achieved with a smooth laminar flow from leading to trailing edges. Anything that interferes with that smooth flow will affect efficiency. Inefficiency here means lost energy. The engine is putting the horsepower into the prop, but it is not moving the volume of water that it should. Another way to look at it is that you are spending good money for fuel, but not getting the speed and distance that you are paying for.

[POG]

Thanks again Ray.  I am aware that a clean surface prop is important.  Mine is not overly impressive.  It is also definitely a sailboat prop with pretty slim blades.  Someone wants to sell me a used 17x12 for $50 that looks and rings OK with much wider blades.  I am hesitant because of the drag.  When you hold this prop up you are looking a an almost  completely filled in circle.  The guy calls it an AP / all purpose prop.  Any thoughts?   

[RayNWanda]

 That photo looks familiar...We left a place just like that a couple of weeks ago. Not much different except the name on the boat.
Be careful of that rear block if it is under the under the bilge. When we bought Abracadabra, she was sitting on the hard blocked up on a crushed rock base. She had been there for about a year and the stands had settled. The blocks did not and she was cracked on both sides. It turned into a pretty extensive repair. On concrete you should be fine, but it is something to be aware of. That area will not support a lot of weight.
There are a lot of different styles of props, and they all perform differently. It may be a workboat type prop, very efficient motoring, but like dragging a 5 gallon bucket when sailing. Will the owner let you take it by a prop shop? Take both props and pick their brains. You have to consider how you plan to use the boat, too. South Pacific distances are long- I would trade motoring efficiency for low drag. Cruising the intracoastal I would want it the other way. The stock props are pretty good all around, reasonably good motoring performance, reasonably low drag sailing.
Whatever you use is going to be a tradeoff. You may get better efficiency motoring but with a penalty of higher drag when sailing, or the other way around. It is difficult to gain in one area and not lose ground in the other with a fixed prop. You are going to have to find what works for the boat, and within those parameters what is going to work best for what you intend to do with the boat.
You might look around and see if you can find a good used feathering prop. We have a folding prop I pulled off because you have to turn it 2,000 rpm to get good reverse thrust. With the 2:1 reduction in the vee drive, we can't get 2,000 rpm. I may decide one day to put it back on, but for now I like the fixed prop better.

[RayNWanda]

 Good looking job.
Ours was delaminated and soaked with engine oil between the layers. The engine had been flooded with seawater and the oil was in the bilge. With that to work with, It was easiest to cut the whole mess out and rebuild it from scratch.

[wedelstein]

I have worked on several P365's. I was very happy with my prop on the 4-108 and 2:1 reduction  with a 17X12 inch prop. I had it measured to make sure. I set to pitch of a Max Prop on another P365 last year at 12". Idealy the P365 should get 6 knots at 2000 RPM witt the 40 hp 4-108 engine

[POG]

Thanks all.  I am now hauled and found that the prop I was told was a 17x12 is actually a 17x10.  It is now at the prop show being pitched up from 10 to 12 - and maybe I can finally be going somewhere!!  Great to have your input.

Carl / POG

[POG]

OOPS...

My prop is at the prop shop not the prop show.

Carl / POG

[POG]

I am back in the water as of about a week.  Pitching up from 17x10 to 17x12 has been a total success.  5 knots at about 1700 revs.  No smoke at higher revs. Perfect!.  To think that this boat has been around for 34 years with a completely inefficient prop!  Thanks again for valuable input.

Departure for the Marquesas still scheduled for April 10, though I might have to be carried on board on a stretcher.

Carl / POG

[Dale Tanski]

Carl,
Thanks for the info and update, but let's review.
How many blade is your new prop?
Thanks...
Dale