how to make planing bottom or improve speed

[pikac]

need help ..i have small wood fishing boat.. i want to improve speed or make him to planing...he is flat bottom with keel..lenght is 4.3 m,width in middle is 1.4 m and width in back is 1.2m...somebody said that only way to make him planing is to cut off keel and to make something like wings on the back of bottom to make same width in back like in middle...now with outboard of 8 ks is going 6 miles..is that maximum speed of this hull?..i wanna at least 10 miles...is it possible...i need your advice..

[messabout]

Your pictures are good. Unfortunately the one we need is not shown. Post a side view picture of the boat. It needs to show whether the bottom curves up as it goes toward the transom ( back of the boat). If it curves upward then planing is not likely to be possible.

One thing the picture seems to show is that the bottom of the boat, the brown colored part, is very rough. Your speed will improve if that surface is made much smoother. It still may not plane but the engine will not have to work as hard to make the boat go. I suspect that this boat is designed as a displacement type because it has a very strong appearing keel. Displacement boats are not designed to plane.

[eyschulman]

Check out Dave Gerr's Propeller Handbook pg. #13 Quarter-beam buttock angle. That is what a lateral view will help detrimine in a rough eyeball way.

[gonzo]

Is the outboard 8 kilowatts?

[groper]

change outboard to 20Kw... it will plane...

[pikac]

thanks messabout..i supouse that is displacement hull..curves goes up in front and in back by transom..but if i change bottom by foam and epoxy is it possible to make planing or semi displacement bottom..??.i shown on next sketch and pics..if i make something like platform or spoiler on back of bottom to make bottom curved down and if i cut little bit of keel in back.....
sorry gonzo i wrote ks for the power of outboard ..is on my language means hp..my mistake..
and what minimum horse power of outboard is needed to plan some boat like this with about 500kg loaded...(if has planing bottom)??
sorry all of you profesionals..i am amateur ..i do this for pleasure and hobby....

[gonzo]

The rule of thumb is about 1HP per 40 pounds. That would mean that a 15hp will get you up on plane. With a flat bottom as you have, less power may be needed.

[PAR]

With such a slight amount of rocker, that hull will plane, though trim issues may arise at certain speeds, this could be handled to some degree with a ventilation plate wing and of course experimentation with trim angles on the bracket.

The biggest issue you have is the small outboard you have not supplying enough power to get you "over the hump". Once up on plane, your 10 HP outboard will do fine (assuming light loads around 1,100 pounds) with mid to high "teens" speeds. 500 kilos on such a hull is a lot of weight, so you'll need 15 - 20 HP to push you over the hump and get you up on plane.

You proposed bottom addition isn't a good idea, for several reasons. It's possible you could get by with just some "shingles" on the bottom just forward of the transom. These in concert with bracket trim and ventilation plate additions will likely get you up on plane, but it's all stuff that needs to be "trial and error".

The first thing you can try is the ventilation plate wing. Purchase one that will also fit a bigger engine, so you can swap it out when you get the bigger outboard. If this doesn't work, then try some trim adjustments (with the wing installed). After these attempts it should become clear if you have enough power to get the boat over the bow wave. I suspect you just don't have enough power, so the next step is a bigger outboard. Once this is installed, you can use shingles (wedges) to trim the bow down at speed.