Extra boyancy

Hi guys,

I have recently just build my second commercial vessel. We have increased the height of the sealed cavities underneath the floor. The second boat is exactly the same side and shape I have just raised the floor in the vessel 120mm from the rear to the front.
My main question is will this increase boyancy of the vessel? We have increased the weight of the vessel and I am hoping this will counteract this and allow it to be similar to the older vessel.

 

Welcome to the Forum Greif.

Can you tell us a bit more about this vessel - what type / size she is, and maybe post some photos please?

Increasing the height of the floor in the boat will increase the 'reserve' buoyancy available (eg if the boat gets swamped), but it will not change the buoyancy (or volume of displacement) of the vessel.
As you have increased the weight, and the buoyancy of the hull is still the same, she will sink deeper in the water than your previous vessel.

Be aware though that you will not necessarily increase or improve the stability of the vessel by raising the height of the floor - rather, the stability would decrease (if the vessel is swamped by a wave) as the weight of the water is now higher up.

 

The boat is 8.7M long at the bottom of the hull it is 2.5M wide and at the top it’s 2.6M wide. This is a shallow V hull at 6 inches. The height of the side is 910mm and has been raised from 800mm in the old vessel. The height of the floor is 400mm compared to 300mm previously. Each vessel has 13 sealed compartments on each side and 8 sealed compartments down the centre, excluding the engine compartment and in the old vessel, the rear bilge. In the new boat we have managed to get the rear bilge compartment to be sealed from any water except from within. (Leaking components)

We have managed to cut down on wood usage in the new vessel by using honeycomb composite where possible. We did also 2 extra 150mm high bearers either side of the vessel to help with trailer rollers because of the weight carried by vessel. We have also added freeing ports to the new vessel to limit the reliance on bilge system.

Overall I expect there to be around 300-500kg of extra weight compared to the previous 3.5 tonne weight. (Including fuel)
The previous vessel could carry around 2 tonne of weight with ease and have loaded upto 3.2 tonne before but was nose heavy.

 

Thanks for the additional details above - do you have any photos that you can post, and / or any general arrangement drawings?
These would help a lot.
Re how she is a commercial boat, what is the commercial usage?

 

As Bajansailor has stated above, the added flotation is added weight, your new boat will have deeper draft due to the added weight.
When I build sealed flotation cavities, I always try to place a drain pipe with a valve in the low corner.
Water has a way of getting into places where you’d think it never would, this allows you a means to check for intrusion without putting a hatch on each one.

 

The compartments will make no difference. They only help when a vessel is flooded.