In a Review of the H41 in Cruising World July 04 it was stated that the boat got to its hull speed at 2800 RPM. I have the hull speed calculated at 7.995 Knts. I have a H41 with a 3 blade standard prop. ( don't have info on its size/pitch ) With the 56hp engine running at 3200 RPM I was only getting 7.3 Knt on the GPS. Anyone with any other infomation on prop sizes and speed /RPM on the H41. Tony
H41 -- Hull Speed
- Thread starter TonyW
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I Wouldn't Put Much Weight In Their Definition
I wouldn't take that 'hull speed' too literally. Basically, any boat at hull speed is trying to drag the ocean with it unless it's a semi-planing hull. I have yet to have a boat that would hit hull speed (with a calibrated knot meter) without wide open throttle and that includes some really over-powered ones. FWIW, on my 40.5 with 50hp Yanmar, I get about 7.0 knots at 3200 RPM with a knot meter reading a bit slow. I get 6.7 at 3000. So, you are in line with mine. BTW, you tend to get some inflated speed claims or wistfull thinking in my experience with club bar talk. Rick D.
I wouldn't take that 'hull speed' too literally. Basically, any boat at hull speed is trying to drag the ocean with it unless it's a semi-planing hull. I have yet to have a boat that would hit hull speed (with a calibrated knot meter) without wide open throttle and that includes some really over-powered ones. FWIW, on my 40.5 with 50hp Yanmar, I get about 7.0 knots at 3200 RPM with a knot meter reading a bit slow. I get 6.7 at 3000. So, you are in line with mine. BTW, you tend to get some inflated speed claims or wistfull thinking in my experience with club bar talk. Rick D.
I have noticed the same thing...
Whenever SAIL magazine reviews a boat--no doubt built by one of their advertisers--they always say "The boat was easily driven to hull speed by the xxHp yanmar turning xxxxx rpm." The only thing I can figure out -- other than they're lying or mistaken -- is that the water is glass flat and the bottom is shiny clean. When I drive my 336 to hull speed under power, I've got black smoke coming out the back.
Whenever SAIL magazine reviews a boat--no doubt built by one of their advertisers--they always say "The boat was easily driven to hull speed by the xxHp yanmar turning xxxxx rpm." The only thing I can figure out -- other than they're lying or mistaken -- is that the water is glass flat and the bottom is shiny clean. When I drive my 336 to hull speed under power, I've got black smoke coming out the back.
GPS Speed...
....is affected by resistance, weight and current. The day must be calm, no wind, no current, no additional weight to affect the speed. CW often tests empty boats that were in a nearby boat show or factory-fresh.
....is affected by resistance, weight and current. The day must be calm, no wind, no current, no additional weight to affect the speed. CW often tests empty boats that were in a nearby boat show or factory-fresh.
Need a diet
Those test boats do not have all the stuff that we bring on board. Count up the weight of everything that you have on board and you will be surprised as to the total amount of weight .
Those test boats do not have all the stuff that we bring on board. Count up the weight of everything that you have on board and you will be surprised as to the total amount of weight .
Buy a motor yacht
I think motor at 3,200 rpm is to much for a Yanmar push a 20,000 lbs or something. If you have water tank full, fuel tank full and the normal weekend stuff on the boat maybe you add a 1,000 lbs to the boat. Is better going down to 2,500 to 2,900 rpm and make 6 to 6.5 knots.
I think motor at 3,200 rpm is to much for a Yanmar push a 20,000 lbs or something. If you have water tank full, fuel tank full and the normal weekend stuff on the boat maybe you add a 1,000 lbs to the boat. Is better going down to 2,500 to 2,900 rpm and make 6 to 6.5 knots.
Sounds about right
Tony, This is probably right. We have a 410 with the same engine. Its LWL is 37.8'. It has a two blade 18" prop and has a computed hull speed of 8.23 knots. We've had it substantially above that while motor sailing with full sails and reasonable wind. Our recently calibrated knot meter is very accurate when compared to GPS SOG and knot readings plus independent handheld. At this engine speed, we burn anywhere from 1.05 to 1.35 gph depending on sea state. Yanmar recommends you cruise this motor (4JH3BE) at 3000, not below. It needs to be able to run hot enough to properly burn the emissions, or something. I was running mine at 2850 and later found that in so doing, you could void your 3 year warranty. At this speed, we have no problem getting up to 8+ knots with a 12 ton boat! The bottom should be clean to do this. And, the motor must be properly serviced! John Richard s/v Jack's Place
Tony, This is probably right. We have a 410 with the same engine. Its LWL is 37.8'. It has a two blade 18" prop and has a computed hull speed of 8.23 knots. We've had it substantially above that while motor sailing with full sails and reasonable wind. Our recently calibrated knot meter is very accurate when compared to GPS SOG and knot readings plus independent handheld. At this engine speed, we burn anywhere from 1.05 to 1.35 gph depending on sea state. Yanmar recommends you cruise this motor (4JH3BE) at 3000, not below. It needs to be able to run hot enough to properly burn the emissions, or something. I was running mine at 2850 and later found that in so doing, you could void your 3 year warranty. At this speed, we have no problem getting up to 8+ knots with a 12 ton boat! The bottom should be clean to do this. And, the motor must be properly serviced! John Richard s/v Jack's Place
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