Motor hp rating for boat

[jacobcraft7]

Re: Motor hp rating for boat

It's hard to tell but it looks like the motor may be a little low. Usually suggested for the antiventplate(just above the prop)to be even with or slightly above the bottom. You should be able to raise it about an inch without any modification just by putting a stick on the transom to hold up the motor while you tighten the clamps.
Typically a 15" motor will actually measure about 17".Some boats will allow the antiventplate to be up to an inch above the bottom.
I usually suggest raising the motor to a point just before ventilation becomes a problem.
Is your prop a 12" pitch? Have you tried trimming up a notch?
Most jon boats will get up on the water pretty easy but sometimes have 4 or 5 keels that may cause drag.
Yours may have a lot of rivets adding to the drag as well.
28 is by no means slow but that 30 mph barrier may be obtainable.

It is 12 inch prop. I haven't tried trimming up yet I will soon. The motor is screwed into the transom as well as clamped on. The dealer put it on for me. The plate is below the boat however.

 

[steelespike]

Re: Motor hp rating for boat

When you trim up it may porpoise.In that case maybe you can move some weight forward.
Also you can buy or make some wedges so you can adjust it for 1/2 a hole.
i had a tiller boat that would stop porpoising if I leaned forward in my seat.
If the motor is bolted perhaps there are holes so you could move it up one.
I did a calculation on the boat that did 31.6.The slip was about 3% possible but
definitely the exception.