Weight vs speed

[Toffen]

Hi!

I have a 25 feet Phantom offshore hull. According to the builder it was built extra solid (and heavy..). The current weight is approx. 2.500 pounds / 1150 kilos incl. engine less driver.

Below the front deck you will find a inner floor between the stringers running from the bow to the aft of the boat. It is made of approx. 15 mm wood. I addition to this the cockpit floor is 25 mm, and runs from 1 meter in front of the dash to the fueltank aft.

In all those two "floors" add some kilo of wood. I plan to cut out the 15 mm plate between the stringers, since the weight in front will be less. The wooden cockpit floor will be replaced with a light weight floor. Maybe divinycell? Other suggestions?

The boat runs very flat and require positive trim. I expect less weight in front of the balance point to be approx. 50 kilos / 110 punds. How much speed will be gained ...??

Cheeeers and thanks, Toffen G

[BarryStrawn]

Add same weight at your new balance point and see how much you slow down.

[Jimboat]

Toffen - you should probably be careful in removing too much of the floor, as the design may rely on floor for some structural rigidity. To answer your specific question, removing 500 pounds (225 Kg) of weight from your hull will indeed allow for increased performance. Running surfaces will be more efficient (better aspect ratio), less wetted surface, and lower required angle of attack; also a better Dynamic Center of Gravity should be attained, improving stability. You should see 3-5 mph better in top speed attainable.

[Toffen]

Hi!

I am sorry for the confusion regarding the weight. I expect to reduce 50-75 kilos in front of the balancepoint. I have checked with Go fast speed calculator, and 2 mph increase may be the result. I will check if the lower deck is necessarry due to structural integrity. One solution is to bore out large holes in this plate, and by this keep the strength and reduce weiht. The cabin floor will be cut ut and replaced with light weight floor.

What kind of material do you suggest for a lightweight floor?

Cheeeers, Toffen G

[jerry]

toffen , you should gain at least 5-7 mph . you my friend are a wizard !!!

[Alan Power]

For a deck I would suggest balsa, it has superior shear and compression strengths, its also cheaper than foam.

Just my .02

[Techno]

Foam is nice but if you need a large span range then it needs stiffeners under it.
A small problem is anything mounted to it needs some special work since you can't do it the same as with wood.

I did notice that your main floor is about 1" thick! That in itself is a weight reduction if it was made of plywood and reduced in thickness. Unless a hull part it don't need to be this thick. Your after floor of 1/2" is what most are using as a main floor.
I'm sure with stiffeners underneath the plywood you could halve both of these- as long as they don't work with the hull.

Both half the thickness = half the wieght. If made from foam 1/4 of the present weight or less.
Since the 1" floor is so thick you might want to check out honycomb. Same problems of mounting as foam but increased skin seperation = better stiffness.