Slamming?

[mick]

I sail a bilge keel Sadler 26 which, of course, is prone to slamming when overpressed. This doesn't bother me, but can anyone explain in simple terms what is happening under the boat when this occurs. I've read explanations before, but I've also read explanations of DNA and I don't get that either.

 

[Lakesailor]

It's like smacking yourself under the armpit. Well, sort of.

 

[MoodySabre]

I think that LS is referring to the amplified sound that is created when air is compressed (like cupped hands) when you trap air under the keels either when slamming into a wave or when you get one keel slightly out of the water when heeling. Goes back in with a thump.

 

[Searush]

Ever done a belly flop into the water? Remember how much it hurts? Well, I guess that translates into the sound & vibration of slamming.

My Pentland does it from time to time - especially when beating into short steep seas (wind over tide, shallow water)

Fin keelers displace the water sideways when dropping off a crest, bilgekeelers have more or less flat bottomed hulls that can hit a large area of the water all at pretty well the same time so it can't easily move out of the way. Water doesn't compress easily so you get high resistance, a big bang & a teeth rattling jar as the boat stops its fall dead.

Shouldn't be a big deal for a well designed & built boat. Hull will be laid up thick enough to deal with it.

 

[VicMallows]

My Sadler 29 Bilge USED to suffer from this horrendously. Interestingly, as more weight has found it's way on board, and in particular since increasing to 40m of chain stowed in the anchor locker, the slamming has all but disappeared. Presumably it no longer 'gulps' pockets of air between the keels.

Vic

 

[Lakesailor]

I could have expressed it better. It's what I used to think of when my bilge keeler used to do it. On the lake you tend to get a short, sharp chop and it's very prevelant if you heel a bit. Nothing to worry about. It's what bilge keelers do.

 

[DJE]

My Sadler 29 does it, maybe I need more chain. If you walk up to the windward shrouds lean out and look down you can see the route of the upwind keel breaking the surface every now and again. When the keel drops back in to the water you get a bit of a slam. I expect the 26 is very similar.

 

[mick]

All is clear. Thanks.

 

[MarkJohnson12345]

My wife does it all the time. Wonder how the house it still standing

/forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif

 

[Lakesailor]

What?

Slaps her armpit?

 

[William_H]

I imagine a bilge keeler has a peculiar slamming motion but my fin keeler has a similar motion in shirt teep waves. The answer is always to get weight forward to stop the bow lifting out of the water so much.

This usually results in me (the captain) sitting up adjacent to the cabin window legs hanging over the side doing that most important of jobs on the boat. The water breaker. Anytime the helmsman or crew get wet it is the water breakers fault. Sometimes I even have to put on a water proof jacket.
Yes it is a light boat and yes the water is not that cold here.

Anyway you need weight forward. You should try to get someone to look at, comment on or photograph your boat in normal sailing mode to seejust how your fore and aft trim is. It is almost certainly low at the stern. good luck olewill

 

[ShipsWoofy]

[ QUOTE ]
What?

Slaps her armpit?

[/ QUOTE ]

It's a Welsh thing /forums/images/graemlins/grin.gif