# Reserve Buoyancy

Discussion in 'Boat Design' started by Tevens, Apr 11, 2011.

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### TevensJunior Member

In vessels such as the Axe bow design or wave piercing bows is there a way of calculating the advantage gained from the extra reserve buoyancy created by these bows? and thus the advantage's which the bow gives in bad seas?

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### daiquiriEngineering and Design

You mean the decrease of buoyancy in the bow?

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### TevensJunior Member

no i mean the gain in reserve buoyancy.

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### daiquiriEngineering and Design

If there is an increase in reserve buoyancy how does a wave piercer "pierce" through a wave?

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### TevensJunior Member

due to the extra volume fore-body there is more buoyancy in the bow,you cannot dis agree.

as a bow enters the wave the extra volume (buoyancy) increase the buoyancy which was there before helping the bow through the wave. buoyancy is a force coursed by the displacement of the water.

I don't want to get into a pointless argument about buoyancy, (though if a wave piercing bow has no reserve buoyancy what is its advantage then?)

it is a fact that wave piercing bows along with axe bows have reserve buoyancy.

I would like to know if any one knows a way of calculating the advantage gained.

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### daiquiriEngineering and Design

I think you are not considering things "everything else being equal" (for example hull length and freeboard height), as should be done when comparing different solutions.
For the same hull length and the same freeboard height, a wavepiercer will have less reserve buoyancy forward. Or else it is not a wavepiercer but something closer to a barge (an extreme example).

How to calculate the advantage? Well if you manage to invent and use that fictitious extra volume, it could reasult in a bigger cargo-holding space - the advantage of which can be calculated through a higher revenue for each cargo-carrying trip.

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### Olavarch. nav.

I dare to disagree. As long as there is some volume above the waterline, there is reserve bouyancy. The only difference I can see between a wavepiercer and a "conventional" vessel is the rate at which said reserve bouyancy becomes effective: On a conventional vessel with flared (i.e. V-shaped) forebody sections the bouyancy increases exponentially whereas on a wavepiercer it's roughly a linear increase or even less when there's some degree of tumble home.

The deep forefoot on an Axebow prevents the forebody from coming out of the water during a bow up movement and thus reduces or eliminates slamming on re-entry.

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### daiquiriEngineering and Design

So, everything else being equal (forefoot depth), which hull type (wavepiercer vs. conventional V-shaped) has more reserve buoyancy in the bow?

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### TeddyDiverGollywobbler

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### Olavarch. nav.

The V-shaped of course. But that doesn't mean the wavepiercer/Axebow has NO reserve bouyancy at all.

OK, I thought that was just a pleonasm.

Last edited: Apr 11, 2011
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### daiquiriEngineering and Design

Knowing the competence of the person, I'm pretty sure that Ad Hoc probably realizes that better than each one of us.

But then you also could have thought that the quote in the post #6 was a typo for example...
Any buoyant bow which rises above the water surface has a reserve buoyancy, though some have much less of it (wavepiercers and axe-bows, for example).

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### Olavarch. nav.

I don't know him personally, but judging from his posts here at boatdesign.net Ad Hoc's competence is unquestionable, no doubt about it.

Maybe it's just a problem of small subtleties in language that causes some misunderstanding with me being a non-native speaker of the English language. I didn't mean to offend anybody or deny anyone's competence and if I did, I want to apologize.

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### daiquiriEngineering and Design

I want to apologise if my post has made you felt like you have to apologise for something.

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Correct, that is true of any hull form.

Want to rethink that? How much do you see here:

http://virginislandswatertaxi.com/boat1.html

http://i48.tinypic.com/2gvtz5d.jpg

No need to apologise, you’re English is far better than my German!

However, I do implore you to read my posts in the thread I gave above. Despite the “heckling” by another member who doesn’t understand the mechanisms behind the reality, you can read what are the real influences in such, apart from marketing.

After you’ve read them, if you have any questions, fire away

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