A Heavy Boat

A conversation over beers with my marina buddy led to a thought exercise on boat weight and ride quality. We could not come to agreement, probably because we are both mechanical engineers and are about as qualified to talk boat design as an intelligent golden retriever; so I come seeking professional opinions.

The core of the question comes down to; how heavy can a boat get before it negatively impacts another attribute to the point where it is no longer a good boat?

This all revolved around 15-17 foot center console bay boats that tend to ride a little rough in chop at speed. The thought is some added weight could reduces the accelerations when cutting through the chop.

I know more weight will reduce carrying capacity, reduce fuel economy and acceleration but what would be the next attribute to suffer with the added weight?

My gut feeling is you could make the hull about 25-30% heavier before it would have gone too far, but id like to know the actual relations of hull design that would create a limiting factor.

Been reading the forums for a while and finally had an excuse to make an account and ask a question.

 

Welcome to the Forum Rowan.

In a nutshell, I think that if you want to ride more comfortably in choppy waters at speed, then you really need more deadrise on the hull, rather than carrying extra weight around with you.
That extra weight is just going to cost you extra $$ at the petrol dock.
Sure, if you take Rent a Mob out with you one day then you will probably notice a difference in the accelerations (and maybe more spray being thrown about) - but is Rent a Mob really worth it when you are paying the fuel bills?

All else being equal (and I am generalising here), a simple boat with zero deadrise aft and amidships will have good carrying capacity and planing speed in flat water, but it will slam terribly as soon as you encounter any rough water.
Whereas a boat with a very deep vee hull will have less carrying capacity, and will require more power to achieve the same speed as the flat bottomed boat, and will achieve less miles-per-gallon (or more gallons-per-mile.... ) but it will have a much superior quality of ride and comfort in a choppy sea state.
You then have to try to find the best compromise in the middle (somewhere between the two extremes above) to suit your requirements - there is no 'perfect' solution, everything is a compromise in boat design.

 

In that size range, 18 degrees of deadrise is about as heavy as you want to get - notwithstanding the Donzi 16 at 24 degrees deadrise, 340 hp, and running 3400 pounds wet.

 

Adding ballast to a15-17’ cc is only going to get you wetter.
Some years back, there was an interesting post on here featuring a small cc boat with a console that moved laterally on a track in the floor to trim it out in various loads and sea conditions.