I have a 1987 37' Hunter. I recently had the cutless bearing replanced along with the strut. The boat yard recommended and installed a 3 blade propeller. The size is 16"x14" on 1 inch shaft. I am only able to rev up to 2,000 rpm, before with a two blade 17"x 10", I was getting the recommended rpm of 3200 tops. I guess they put on the wrong size propeller, or is this due to the cutless bearing being new? I would greatly appreciate your feedback Thank you!
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My guess is you should have lost about 1000 rpms
My guess is that you should have lost about 1000-1200 rpms +/-. If you would have had the same size prop but 3 blades that would have knocked you down by about 250-300 rpms. You went from a 17 to a 16 so that would have been a push. For each degree of pitch you would loose about 250-300rpms/inch. So it looks like you are right on. (WRONG Prop). Not to mention that you can't power any better, you now sail slower too.
My guess is that you should have lost about 1000-1200 rpms +/-. If you would have had the same size prop but 3 blades that would have knocked you down by about 250-300 rpms. You went from a 17 to a 16 so that would have been a push. For each degree of pitch you would loose about 250-300rpms/inch. So it looks like you are right on. (WRONG Prop). Not to mention that you can't power any better, you now sail slower too.
L
LaDonna Bubak - Catalina Owners
3 blades
I get really suspicious when a yard suggests I should change something on my boat. Normally, it's really expensive and completely unnecessary. More often than not, the correctly sized & pitched 2 blade props are just as, if not more, effective as 3 blades. Steve is right that 3 blades do cause more drag and they only give you a power boost in relatively heavy seas. Usually if the seas are heavy, you'll be sailing anyway to decrease unpleasant motion. I would seek out a professional prop shop & get their opinion. They may be able to repitch your prop to give you the speed you need. Rob's prop was so off that he could only make about 4 knots in calm water. He had it repitched & now makes 5.5. LaDonna
I get really suspicious when a yard suggests I should change something on my boat. Normally, it's really expensive and completely unnecessary. More often than not, the correctly sized & pitched 2 blade props are just as, if not more, effective as 3 blades. Steve is right that 3 blades do cause more drag and they only give you a power boost in relatively heavy seas. Usually if the seas are heavy, you'll be sailing anyway to decrease unpleasant motion. I would seek out a professional prop shop & get their opinion. They may be able to repitch your prop to give you the speed you need. Rob's prop was so off that he could only make about 4 knots in calm water. He had it repitched & now makes 5.5. LaDonna
D
David
Prop size
Your pitch is much too high. Contact a prop shop. They usually have a computer program that, with vessel and engine input from you, can provide the correct pitch and diameter. They can only repitch a bronze prop two sizes. I would try to exchange your current 3 blade for the correct size. There are some benefits to a three blade prop ( I installed one last year ) but not if you race alot.
Your pitch is much too high. Contact a prop shop. They usually have a computer program that, with vessel and engine input from you, can provide the correct pitch and diameter. They can only repitch a bronze prop two sizes. I would try to exchange your current 3 blade for the correct size. There are some benefits to a three blade prop ( I installed one last year ) but not if you race alot.
K
Kevin
To large of prop.
Dear Gus, Thank you for your note. In looking at the old two blade specs and looking at the new three blade specs, I would find it highly unlikely that the cutlass bearing is the culprit. I would think that the total reason for your reduction Rpm’s is totally the increase of pitch and the additional blade. The boat yard has increased the load, the propeller can produce, by over 30% when they went to the three blade. We would have suggested to use a 16” x 10” or 11” max. If you use the current propeller for a long enough period of time, you could see excessive carbon build up and injector problems. I would suggest that you remove the fixed three and have a prop shop reduce it’s pitch. Depending on the style of propeller you have they may be able to remove as much as the needed 3 inches. Good luck. Sincerely Kevin.
Dear Gus, Thank you for your note. In looking at the old two blade specs and looking at the new three blade specs, I would find it highly unlikely that the cutlass bearing is the culprit. I would think that the total reason for your reduction Rpm’s is totally the increase of pitch and the additional blade. The boat yard has increased the load, the propeller can produce, by over 30% when they went to the three blade. We would have suggested to use a 16” x 10” or 11” max. If you use the current propeller for a long enough period of time, you could see excessive carbon build up and injector problems. I would suggest that you remove the fixed three and have a prop shop reduce it’s pitch. Depending on the style of propeller you have they may be able to remove as much as the needed 3 inches. Good luck. Sincerely Kevin.
T
Tom
Gus, what knuckleheads changed your prop
I'm not talking about from a 2 blade to a 3 blade, because there is nothing wrong with a 3 blade and if you'd like more umphh! when powering into head seas and you don't care about the little extra drag under sail. But going from a 10" pitch to 14" !!!...That is not even in the ball park .....that is way too much, especially since the old prop (2-blade 17x10) seemed to reach the recommended 3200 RPM's max.....It sounds like the yard had it sitting around and figured they could off load it (make money) on you....don't stand for it, insist that they replace it with a proper sized propeller....I'm sure any of a number of prop shops would be welcome to recommend a correct size, use that information and have your yard change it at NO COST to you If I had to guess a closer size .... Going down in diameter 1inch, but adding a 3rd blade causes about a "wash"....but adding 4 more inches of pitch caused the max RPM to go down by 1000 RPM's. I would agree with Kevin. "to use a 3 blade 16” x 10” or 11” max."
I'm not talking about from a 2 blade to a 3 blade, because there is nothing wrong with a 3 blade and if you'd like more umphh! when powering into head seas and you don't care about the little extra drag under sail. But going from a 10" pitch to 14" !!!...That is not even in the ball park .....that is way too much, especially since the old prop (2-blade 17x10) seemed to reach the recommended 3200 RPM's max.....It sounds like the yard had it sitting around and figured they could off load it (make money) on you....don't stand for it, insist that they replace it with a proper sized propeller....I'm sure any of a number of prop shops would be welcome to recommend a correct size, use that information and have your yard change it at NO COST to you If I had to guess a closer size .... Going down in diameter 1inch, but adding a 3rd blade causes about a "wash"....but adding 4 more inches of pitch caused the max RPM to go down by 1000 RPM's. I would agree with Kevin. "to use a 3 blade 16” x 10” or 11” max."
No upshifting!
I totally agree with Tom from Stamford here. When I worked at a speedboat manufacturer, guys would phone up and ask how they could get more RPMs out of their engines– they were running huge big-block Fords and Chevys at 5500+ RPM (essentially redline) and started blaming the engine guys. I would say, 'Did you ever think of the prop?' Then it was me giving these lifetime gearheads a lesson in prop pitches. Every increase in pitch is like shifting up a gear in your car. You can no longer start out as well but given the same RPM your top-end speed will be higher. This carries with it all sorts of suggestions of better fuel mileage and reduced engine wear– all true in cars. To gearheads with ski boats in flat water, hearing this is like manna from Heaven. There is, however, NO correllation of this to displacement sailboats. No matter what your powerplant the top speed of a displacement (non-planing) sailboat hull is essentially fixed– figure it at 1.36 times the square root of the waterline length. A Hunter 37 will probably be about 7 or 7-1/2 knots. Asking a boat like this to power past hull speed is an exercise in futility. (A friend with a Tartan 33 once found that his fuel consumption DOUBLED whilst pushing the boat a 1/2-knot past hull speed.) Sailboat prop requirements ought to be kept modest. If you are losing any SUBSTANTIAL rev's due to increased prop pitch and find you can no longer rev the engine to where you used to, or cannot achieve hullspeed without a dramatic increase in fuel consumption and/or black smoke, you have MOST DEFINIELY got the wrong prop. Also, the third blade ought be no problem other than to increase drag a little under sail, although there is a loss wheeling the extra blade around with the same horsepower as well. Cruisers who do a lot of powering or motorsailing can really benefit from a 3-bladed prop. Reversing is also more efficient. But there really ought to be no dramatic difference as reported by Mr Sanchez. I too would have gone with 16 dia. and 11 or 10 pitch for a 3-blader. So I also agree with Tom's suggestion that Gus get outside professional opinion and then approach the yard about reverting the boat to its PROPER spec and giving them the $300 Tobin bronze prop they certainly must have had lying round back to them to collect more dust. In return they ought to refund the money to a customer dissatisfied with changes they suggested and convinced him to accept. If there is any trouble, casually mention that a certain local attorney is a regular guest on the boat and asked what the h*ll has been wrong with it lately. [wink] JC
I totally agree with Tom from Stamford here. When I worked at a speedboat manufacturer, guys would phone up and ask how they could get more RPMs out of their engines– they were running huge big-block Fords and Chevys at 5500+ RPM (essentially redline) and started blaming the engine guys. I would say, 'Did you ever think of the prop?' Then it was me giving these lifetime gearheads a lesson in prop pitches. Every increase in pitch is like shifting up a gear in your car. You can no longer start out as well but given the same RPM your top-end speed will be higher. This carries with it all sorts of suggestions of better fuel mileage and reduced engine wear– all true in cars. To gearheads with ski boats in flat water, hearing this is like manna from Heaven. There is, however, NO correllation of this to displacement sailboats. No matter what your powerplant the top speed of a displacement (non-planing) sailboat hull is essentially fixed– figure it at 1.36 times the square root of the waterline length. A Hunter 37 will probably be about 7 or 7-1/2 knots. Asking a boat like this to power past hull speed is an exercise in futility. (A friend with a Tartan 33 once found that his fuel consumption DOUBLED whilst pushing the boat a 1/2-knot past hull speed.) Sailboat prop requirements ought to be kept modest. If you are losing any SUBSTANTIAL rev's due to increased prop pitch and find you can no longer rev the engine to where you used to, or cannot achieve hullspeed without a dramatic increase in fuel consumption and/or black smoke, you have MOST DEFINIELY got the wrong prop. Also, the third blade ought be no problem other than to increase drag a little under sail, although there is a loss wheeling the extra blade around with the same horsepower as well. Cruisers who do a lot of powering or motorsailing can really benefit from a 3-bladed prop. Reversing is also more efficient. But there really ought to be no dramatic difference as reported by Mr Sanchez. I too would have gone with 16 dia. and 11 or 10 pitch for a 3-blader. So I also agree with Tom's suggestion that Gus get outside professional opinion and then approach the yard about reverting the boat to its PROPER spec and giving them the $300 Tobin bronze prop they certainly must have had lying round back to them to collect more dust. In return they ought to refund the money to a customer dissatisfied with changes they suggested and convinced him to accept. If there is any trouble, casually mention that a certain local attorney is a regular guest on the boat and asked what the h*ll has been wrong with it lately. [wink] JC
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