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post #21 of 22 Old 07-09-2018
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Re: How Fast Should My Boat Go Under Diesel

Originally Posted by Baysailor34 View Post

Engine - Yanmar 2GM20F
HP - 16
Boat - Island Packet 29
LWL - 27.58
Beam - 10.83
Displacement - 10,900 (empty)

Maybe some haven't significantly re-read the initial post.

A 16 HP engine on a full keel, heavy boat is never going to push it anywhere near Hull speed.
Is it?

I would suggest it's an old boat when engines were defiantly "axillary power" not designed as main power.

My boat has a similar displacement but fin keel and it has a 57HP engine in it.

To consider his to go the same speed as mine is not looking at physics. Unless he has added something to his fuel... Maybe cocaine.

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post #22 of 22 Old 07-09-2018
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Re: How Fast Should My Boat Go Under Diesel

This is something of an old thread, but Mark is right, this is too small an engine to push this boat to hullspeed. My boat weighs virtually the same weight as the OP's boat, and probably has the same or less wetted surface. It has an easily driven hull form that is optimized for reaching speeds which is similar to a semi-displacement hull form that is optimized for powering. I have the three cylinder version of the same engine (a 3GM30F, rather than the 2 cyl in the O.P's I.P.). It pushes my boat at around 6.3 knots in flat water at around 2,900 rpm cruising speed, which is substantially less my boat's 7.6 knot hull speed. Even wound up to 3,200 rpm, I only get into the 6.8-6.9 knot range. Arguably my prop could be pitched a little more aggressively and have a little more area, but even so, I seriously doubt that I would get much over 7 knots since the engine seems to be self limiting around 3500 rpm which is below the point that the mechanical rpm limiter kicks in, which suggests that at 3,500 speed is limited by HP and not the prop.

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