Buoyancy vs Weight

[halfboat]

Hi,
I could really use some input on this.
I have a 22’ walkaround (Grady style) with a 225 Honda on a stainless bracket. My problem is that the boat is a bit narrow and the aft sits fairly low in the water. Performance is ok, (with trim tabs) but a little slow to plane when loaded. My question is: if I replaced the bracket with a sealed hull extension that served as a full width swim platform and engine bracket, would this help buoyancy and performance, or would it just add more weight to an already @$$ heavy boat? I can guess that performance would be increased because you are effectively lengthening the hull. But would buoyancy be increased enough to justify the time and expense, and for that matter, would the boat float any higher?

Thanks for any thoughts or input.

[jehardiman]

1. It is very difficult to get the weight too far aft on a small open planing boat. If the running angle is ~5-10 degrees you are in the ballpark. Try changing the thrust angle of the OB if you think the bow is too high, but most likely this will have a detrimental effect of performance.

2. Increased weight will decrease performance with fixed horsepower. Period. The need for a higher planing angle and/or speed to get up on plane is an effect of the added weight, not the hull length.

3. Increased wetted surface (i.e. length) will decrease performance of small planing boats. Resistance of a planing boat is not a waterline length problem, it is a wetted surface to weight relationship only.

[Eric Sponberg]

On the other hand, there have been many successful stern extensions on yachts, and done smartly on a small boat, it can work. Generally, you will gain more in buoyancy than you will add in weight, and this will affect the still water and running trim of the boat. Added weight and hull length will tend to decrease speed, but the added buoyancy will reduce trim and tend to increase speed. Certainly, optimize the outboard tilt angle first before making the structural modification, and you might want to consult with a naval architect to make sure the size of the addition and its structural details are sound.

Eric

[ted655]

You may get a solution with the prop on your motor. Check archiveshere, but I think the cav plate has to be raised 1" for every foot of extension. Get that right, then, get with a prop man & maybe change dia. & pitch.
Tou're just after a better hole shot right, not trying to level the boat? If leveling the boat is the project, then a "pod" of some sort would be in order.