Displacement boat - speed

Hello? Does anybody have experience with adding stern (something like on menorquin) plate on boat like this one from photo? What I can except regarding the speed and stability? Currently, top speed with 100hp is 8.5kn.

 

I plan to add stabilizer like on this photo

 

Many current "menorquinas" are built with aft platform. Very useful as bathing platform, I do not think it will improve the speed or stability.
If what you want to add are sponsons, the result can improve trim and stability. With a speed of 8 knots do not think it will improve the speed.

 

My plan is to add sponson, length about 4m

 

Then you should explain the problem you have, what you want to achieve with sponsons, to calculate its volume, shape and position.

 

I want to achieve higher speed and stability. At top speed the trim is about 60cm.

 

You say that trim at top speed is 60cm. Does that mean that the bow of the boat is 60cm higher than when the boat is at rest? Or does that mean that the stern is depressed 60cm ?

 

The stern is depressed aboat 60cm

 

What is the length of the boat?

What is the speed with 50% or 75% throttle?

 

L=11.4m,
Lwl=10.8m,
B=3.35m,

Propeller: D=650, H=580,
Enigine 100hp, 2000rpm, ratio 1:2.9,

1000rpm - 6.5kn

 

Duco84,

Your vessel is just right the way it is. It is fit for purpose. Adding sponsons will greatly increase wetted surface & drag, so you would probably need more horse power.

To illustrate your predicament, there was a tourist on holiday & driving a hire car, who had become lost in the countryside. He stopped to ask a local farmer the directions to return to his hotel.

The farmer was silent for a few moments & then said to the tourist, " Well, if you want to get back to your hotel, I would not start from here".

There is this Jetpac system. http://sealionmarine.com/products_en.php

 

A 5% trim is a lot. You are right, you should add volume aft to reduce that trim, or change the weight distribution. I think the latter is more advisable, if possible.

 

I agree with pericles .This boats original design was for 30hp motor for efficiency at around 6 knots .What happens when you add more power is that it actually gains lift on the flat mid section and lifts the bow and hence pivots and sinks the stern.You may add water tanks forwards on each side .This may improve stability and trim .
I think you need just to enjoy going slow and sipping fuel or get another boat that fits your need for speed

 

You might finish up with a boat that handles quite differently with the seas running with it, too.

 

this solution is usual here since 1983. Now all new boats of this type are made so. This geometry allows to keep intact the quality of stability at low speeds typical of traditional fishing boats, and you can install more power and bring the boat at speeds greater than the speed of displacement.

http://www.cantierinavaliposeidon.it/flotta/25o.swf


https://www.youtube.com/watch?v=4fZj240Phfo