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Question for PYI: How to find out size and pitch

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L

LeeHound

I got recommendations for my Sabre32 from PYI according to my current prop and engine specs, but in order to avoid costly and time-consuming hauling for fine tuning I would like to know if you or others have lists with specs for a specific boat type that reflect the experience that people had with specific props and sizes, so we are as close to the ideal combination as possible without costly trial and error haulings? Another question in this context: how do you generate your recommendations, or: how practice oriented are they? Lee
 
K

Kevin

Based on loads

Hello Lee, Thank you for your note. We use numerous methods of calculating pitch. The most common is the comparison of data obtained from one vessel to the next. We also work with engine make/models and transmissions to produce loads, which we can then calculate propeller load capacities. Of coarse each of us here have a bag of bones we can throw on the floor to help us, but all in all we factor pitch using theoretical loads. One of a great many problems we encounter with pitch is the difference between like boats and like installations. It’s very difficult to compare a day use boat with an owner that say’s his vessel is to factory specs but its found he tows a 12’ dink and 3,000 pounds of extra gear, engine driven refer, two 100 amp. Alternators… In this case we may see speed differences of 1.5 knots and pitch differences as much as 4 degrees. We also see many problems with opinions between boat owners. Some choose to have an engine run at very low and heavily burdened loads. Others choose to run them at very high lightly loaded Rpm’s. PYI is very careful to keep those opinions/wishes of the owner in mind when we recommend but we always try to recommend our pitches based on the engines ratings. We are concerned for the customer’s performance achievements but equally concerned for the longevity of the motor. Hope this helps. Kevin
 
R

Rick

Multiple haulouts...

...are just part of the cost of getting a Maxprop. At first splash you will be thinking no way can this be right - you will either have black smoke (too much pitch) or poor performance (not enough or just right). So you make adjustments to make the smoke go away and then realize just how inefficient flat blades really are. I was very disappointed to find out that never again will I able to motor at hull speed because of this $2000 mistake. Ever try to get a refund on a propeller? The first thing they ask is if it's ever been in the water. (Duh! How else would I have learned that my old fixed prop worked better?) I guess getting them wet violates the warranty even though satisfaction was guaranteed. (And they are very satisfied with my money - so no refund). Live and learn. For me, never again will I do business the company that sold me the prop and I am more than happy to share my experience with anyone considering a Maxprop.
 
T

Trevor

PYI got it right the 1st time on my boat

The pitch was right the first time on my Catalina 36... but maybe I was lucky. I think it's fairly common to make adjustments after installation, but it's usually pretty easy to get it right the 2nd time based on symptoms from the 1st time. Personally, I've found the folks at PYI to be very customer-centric and great to deal with. I love that prop! Best of luck, Trevor
 
D

Doug T.

Lee...

Lee, you might want to check out the Sabre e-mail list that's run by sailnet. There's bound to be a Sabre 32 owner on there that's installed a maxprop before. Perhaps check the archives there -- it's a frequently discussed topic.
 
Jul 1, 1998
3,049
Hunter Legend 35 Poulsbo/Semiahmoo WA
PYI Rates "A" for Support

Lee - For what it's worth, I'd rate PYI an "A" for customer support and talking one through problems or decisions and for me that's a real plus. When I put on my Max-Prop about 13 years ago I also installed a PSS shaft seal. If you plan to keep your boat for a while and you like to sail more than motor, and like to sail fast, then a feathering/folding prop is for you. Last year we went to Alaska and had to be back by date certain and therefore had to cover a lot of ground in a very short time. We did 2,222 nautical miles in 77 days with 2/3 motoring and 1/3 sailing. Our motoring speed (loaded down with a Hunter 35 and 1.5 year old bottom paint was about 6 knots, or maybe a bit less) but our speed over ground for the trip was 7 knots! This was per GPS and figures were kept by the first mate/admiral. It was her job to determine the schedule and my job to keep it! The higher speed over ground can be attributed to two things: going with the tide (current) whenever possible and sailing at above hull speed - which we did quite a bit of. One memorable day we "flew" down Chatham Strait for almost all day flying the spinnaker while pulling a huge wake and doing 8 and 9 knots over ground. This latter factor can only be achieved easily with a feathering prop. And another factor - it's quiet! No shaft noise. And no wear and tear on the driveline. Sail more, motor less, and save wear and tear on the engine. We're one pitch off from the original install but the boat is also much heavier than factory. The pitch change came one year, a few years back, during a regular scheduled haul out for bottom paint so no additional cost. On the other hand, the nice thing is that one can actually change the pitch - you can't do this with a fixed-blade prop without taking it to a prop shop! To me, the holistic experience of a boat with a low-drag prop is worth all the effort in getting there - second haul out or no. Obviously my experience has been positive.
 
J

Jose Venegas

MaxProp not so efficient

Lee, check out my response to 2 or 3 blades in this forum. Maxprop and Autostream feathering props have flat blades. That is OK for drag but not so good for power transfer. To be hydro dynamically efficient, a prop blade needs to have a twist with decreasing pitch as you move away from the shaft. This is needed because the rotational speed of the blade relative to the water increases as you move away from the shaft. Thus to maintain a proper angle of attack, the blade's pitch should be decreasing with radius. The lack of twist in a prop blade results in improper angle of attack, except at one radius, leading to flow separation and potential cavitation. If you want to decrease drag consider a folding prop like the Gori 3 blade
 
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