structural issues

[30boat]

Why would a well known and respected builder such as Westerly build engine boxes not laminated to the bottom of the boat and leave them to float instead?
In my boat the engine box sides move to a noticeable degree when conditions get rough .
I'm going to epoxy the whole thing to the bottom this winter to make the structure whole as it should be.
The boat feels very strong but my previous boat ,a balsa sandwich D.Peterson design built in China was very silent underway,apart from some creaking at the mast step, while the Westerly isn't.There was a lot wrong with the quality of construction with my older boat and I know it wasn't nearly as strong as the Fulmar but it felt stiffer.Is this a normal caracteristic of sandwich construction?

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[vyv_cox]

No idea at all why Westerly built it the way they did, it might simply be to save money on production time. On the other hand, it might be that restricting hull flexing could lead to high stresses and resultant cracking. I would be very careful before making structural changes like this. History is littered with examples of the problems that can result from making 'improvements' to successful designs.

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[richardandtracy]

Agreed.
Stiffer areas attract load. When glassing in the base of the engine box it's highly likely that the strength will not increase in proportion to the stiffness due to the inherent weakness of a glass-glass bond after a few years of curing. Also stiffness increases as a cube of material thickness, while strength is a squared relationship - increasing less fast than stiffness as the thickness increases. A safer option would be to stiffen up the sides of the engine box with a frame around the bottom or something similar.

Almost all modern aircraft have the same miniscule sized fuselage frames througout their length - it's to stop attracting excessive load to a hard spot in the aircraft. It prevents embarrasing events - like the aircraft blowing up in mid air. The same principles apply to boats - they are very lightweight (for their size) and flexible structures too.

Regards

Richard.


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[billmacfarlane]

Before you do anything why not put your proposal on the Westerly owner's web site ?

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[Guest]

I would be inclined at most to glass a frame at base and then spring clip the box down to it so that it doesn't move, but also does not impair the flex / movement of the hull area.
But I would refrain from glassing it in permanently, if only to ensure that access to the engine in event of major repairs is still available !!!!!


<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[graham]

Possibly some soft rubber glued to the bottom edge of the box will cure it.

I would be wary of bonding it solidly to the hull ,the strength of boats lies partly in there ability to flex .



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[Avocet]

I'd just like to add the considerable weight of my ignorance to the above! I'd be VERY wary of doing anything that might locally stiffen the hull in an area where it wasn't supposed to be stiff! It's possible you might end up with stress cracks forming on the outside of the hull along the edge of the line where the engine box is bonded to it because you will have suddenly stiffened an otherwise (I'm guessing here) pretty floppy area. I'd be inclined to research the issue further personally!

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