Rebuilding Wellcraft Excalibur 45 hull. Had 315 Yanmars, don't know gears or ratios, with PulseDrive surface piercing system. Did 37-38mph. Installed 440 Turbo Yanmars using same PulseDrive surface piercing system. Theoretical calc's say 48/49mph with existing equipment and 13% slippage. Weight 18,500lbs, New bottom job, 45'x11', gears-ZF 2.00 to 1. Props are trued to 21x30, tachs read 3400(p) 3500(s), top speed 41mph. Anyone got any idea what the problem is?
Mph lost somewhere
- Thread starter TSpeedy
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I am sure Footloose will be chiming in here, his Harley has Arnesons and we are all familiar with his adventures with this drive system. I haven't had any experience with surface piercing drives, but my understanding is that the props have to be trimmed up to the point where they are only halfway in the water, otherwise the engines are overloaded. Do you have somebody there who is familiar with running surface piercing drives? If so, I recommend getting him to go out with you and assessing the situation.
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My guess is that the gear ratio needs to be more aggressive with the significant increase of horsepower. What are the WOT RPMs of the 440s vs the 315s.
Sorry, Don't know how to pitch surface piercing props. Ollie probably has some tips.
Theoretical speed and actual speed never seem to be that close. Not familiar with your boat but many boats seem to have a certain limit to their speed because of the hull. Could be anything from a hook in the hull or design. It also takes quite a bit of HP increase to see a measurable increase in top end speed. In my smaller boat, I increased HP and torque about 30% and don't see a particular increase in top end.
Theoretical speed and actual speed never seem to be that close. Not familiar with your boat but many boats seem to have a certain limit to their speed because of the hull. Could be anything from a hook in the hull or design. It also takes quite a bit of HP increase to see a measurable increase in top end speed. In my smaller boat, I increased HP and torque about 30% and don't see a particular increase in top end.
tugboat kevin
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we run a poker run boat with arnsons theres quite a learning curve to driving these as in the faster you go you have to lower the drives(as the hull lifts up onto the surface)and they do not like to be adjusted at speed almost threw us out a few times so you set the drives to a good number on the indicators for what ever speed you plan on running then drop the hammer we can accellerate from 40 to 140 in 10 seconds
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