Do-it-yourself marine architecture

[MikeJohns]

This gentleman is trying to move his COB forward to balance the boat having removed some weight from the stern. The tank is off an air compressor. The ingenuity of the do-it-yourselfer ! Professional advice was not sought. I had a look and the welding , it looks good ! The tank is not true to the waterline but slopes down by a few degrees.


Perhaps you can have a few guesses at how this will perform.

[marshmat]

Well..... I wouldn't do that to my boat.....
Assuming it's supposed to be a displacement hull, he might get a bit of the bulbous-bow effect, but the turbulence.... oh, the turbulence, and the amount of drag that thing might make with such a flat tip.... I'd be interested to see how the sea trials turn out, for sure.

[gonzo]

If he removed weight from aft, the Center of Gravity moved forward automatically. By adding floatation forward he is incereasing the effect. However, tha wave and eddie forming may ruin the boat's performance.

[Sander Rave]

Hmmm... it looks like a kamikaze thing to me. Seen things like this in pre WW1 navy documentation.

Was the owner wearing a turban?!

[Tim B]

Why not just take some weight out of the bow? I'm sure he doesn't need all that 500m of anchor chain! (1500 feet for you American lot)

Tim B.

[Stephen Ditmore]

I wonder if there's some material he could put all over it that would wear away progressively until it had shaped itsself. When it looks about right he could stop the wear by spraying a layer of resin on it...

Please take this as free-associating / brainstorming. Not professional advice or endorsement. But if he want to have some fun, and it's his boat...

[Thunderhead19]

I've seen this done sucessfully on smallish purse-seiners. It doesn't seem to have a negative impact on performance, and is used, i think, to keep the bows from plunging quite so much while fishing. Any thoughts on this?

[Guillermo]

My goodness..! There are creative guys around, aren't they?
Bulbous bows for small boats has been a matter of discussion for a long time and benefits/loses equation, taking in account hydrodinamics, in-waves sailing behaviour, intended sailing scheme, etc., has to be always carefully evaluated on a case to case basis. Even properly designed bulbs have been of little (or none at all) advantage in some cases.
To add a bulb just to move the COB forward and doing it the scrapper way, it's most amazing. Most probably this gentleman's initiative is going to be a real mess from the point of view of hydrodinamics and sailing, not to talk about aesthetics!

[MikeJohns]

Originally Posted by gonzo

If he removed weight from aft, the Center of Gravity moved forward automatically. By adding floatation forward he is incereasing the effect...........

Gonzo
Too much red wine???
After removing the heavy haul winch from the stern the boat assumed a severe bow down attitude (because the COG moved fwd)
COB was now aft of the COG for the designed trim , by adding bouyancy fwd he is correctly shifting the COB fwd relative to the COG. This will trim the vessel up by the bow.

[cyclops]

If the bow goes down, make it come back up. Sounds right to me.

[MikeJohns]

Originally Posted by Stephen Ditmore

I wonder if there's some material he could put all over it that would wear away progressively until it had shaped itsself. When it looks about right he could stop the wear by spraying a layer of resin on it...

Yes the shape leaves something to be desired, I wonder if that would produce a nice shape? Could paint 20 cans of ablative anti-fouling on the protuberance and watch it wear away to an ideal shape . Better rush off and have a look at the rocks in the river to test this one

The gentleman was also convinced that the buoyancy from the cylinder would increase the deeper he attached it. Now that would introduce a few complex differential equations into hydrostatics not just hydrodynamics !


Heres another one to think about ..........
Submarines have to make themselves lighter as they dive.

[gonzo]

OOps, typing without checking myself. You are right.

[george allard]

If you fill it with a lot of air pressure and put a dump valve on the front, it would make a great reverse gear.

[Grant Nelson]

As an aside, I have seen this kind of addtion (more hydrodynamicaly shaped of course) attached to a relatively flat bottomed (typical Dutch) power cruisers to provide a vertical space to insert a bow thruster... in that case I am not sure if it was an add-on or part of the original design, and if it was, if they consider the effect on the CoB...

[lewisboats]

Originally Posted by Guillermo

My goodness..! There are creative guys around, aren't they?
Bulbous bows for small boats has been a matter of discussion for a long time and benefits/loses equation, taking in account hydrodinamics, in-waves sailing behaviour, intended sailing scheme, etc., has to be always carefully evaluated on a case to case basis. Even properly designed bulbs have been of little (or none at all) advantage in some cases.
To add a bulb just to move the COB forward and doing it the scrapper way, it's most amazing. Most probably this gentleman's initiative is going to be a real mess from the point of view of hydrodinamics and sailing, not to talk about aesthetics!

At a guess...from the picture...this is a powerboat...which might change things a tad.