Even if the hull was damaged and somehow leaking inside the cofferdam, the pump located there would only have to deal with a small volume of water compared to potentially much larger leaks in the rest of the hull.
I would guess that you are much more likely to get holed, or have a plank butt come loose, or have a seriously leaking seam, in other areas of the hull. Or, it seems most likely, get swept by a nasty wave. But in these cases, the coffer would keep the machinery dry.
Getting a bit off topic, I'm afraid. Sorry. I'm done.
-Tom
--- In electricboats@yahoogroups.com, Rob Johnson <dopeydriver@...> wrote:
>
> I'll be spending a great deal of time with my boatbuilder , who is very
> experienced in these sorts of conversions (but not electric power).
> I would imagine that he would make up an engine box.
> The downside of course is , what if the hull is compromised at the engine box ?.
> But , I'll be guided by the boatbuilder , that is his field.
> Regards Rob J.
>
>
>
>
> ________________________________
> From: Tom <boat_works@...>
> To: electricboats@yahoogroups.com
> Sent: Fri, 25 March, 2011 11:38:53 AM
> Subject: Re: [Electric Boats] brush or brushless?
>
> Have you considered isolating the machinery space with a cofferdam?
>
> This way even if the boat was flooded above the height of the motor, the
> machinery space is not affected. It could even have its own high capacity pump,
> if you are a belt and suspenders sort of guy.
>
> It would take some clever design work to make maintenance work possible, but
> that's part of the fun.
>
> -Tom
>
>
> From Wikipedia:
>
> A cofferdam may also refer to an insulating space between two watertight
> bulkheads or decks within a ship. A cofferdam may be a void (empty) space or a
> ballast space. Cofferdams are usually employed to ensure oil or other chemicals
> do not leak into machinery spaces. If two different cargoes that react
> dangerously with each other are carried on the same vessel, one or more
> cofferdams are usually required between the cargo spaces.
>
>
>
> --- In electricboats@yahoogroups.com, Rob Johnson <dopeydriver@> wrote:
> >
> > Myles , in my case its just that whatever water has found its way in to the
> > bilge is really going to be sloshing around.
> > Today is a mild day here , with 25knots winds and 5 metre seas.Sometimes those
>
> > waves , that swell seems to get very close together and steep , so you really
> > get bounced around.
> > Every time I go out I try to get everything secured in the cabin , but
> > invariably , we will be climbing up a steep wave , and I hear the sound of
> > "stuff"rolling around in the cabin.
> > And thats about the time I've got to put in a tack , and I've just hooked a
> >nice
> >
> > big whiting.
> > Regards Rob J. ÂÂ
> >
> >
> >
> >
> > ________________________________
> > From: Myles Twete <matwete@>
> > To: electricboats@yahoogroups.com
> > Sent: Fri, 25 March, 2011 2:44:13 AM
> > Subject: RE: [Electric Boats] brush or brushless?
> >
> >
> >
> >
> > If you think your motor installation will be exposed to water, do not use a
> > brush motor.
> > Having said that, there are many electric car owners who use brush motors, many
> >
> > of which are highly exposed to rain splashing from the street and some of which
> >
> > have forded thru water without incident. However, in those instances, there
> >is
> >
> > relative wind velocity to help clear out the moisture. IN our case, that wind
> >
> > velocity is limited to whatever air ducting you provide.
> > If you want to go with a brush motor and an outboard installation is not
> > suitable, then it is highly recommended to belt-drive your prop shaft, locating
> >
> > the motor above the output shaft. There are several installation photos on
> >this
> >
> > site (e.g. this one) which show configurations like this. You could also
> > enclose the motor in a ducted shroud with only the wires, mounting hardware and
> >
> > motor shaft exiting, making risk of water splash entry non-existent.
> > You could locate your motor a good foot or more above the prop shaft---plenty
> >of
> >
> > height to not worry about anything but very significant bilge infiltration
> > conditions…and at that point your motor working might be the least of your
> > worries…
> > ÂÂ
> > -Myles Twete, Portland, OR.
> > ÂÂ
> > From:electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On
> > Behalf Of affordableacadia
> > Sent: Thursday, March 24, 2011 4:38 AM
> > To: electricboats@yahoogroups.com
> > Subject: [Electric Boats] brush or brushless?
> > ÂÂ
> > ÂÂ
> > Hello
> >
> > I am new to this forum but am building an 18' electric boat for recreational
> > lobstering here in Maine. I had a Mars ME0909 picked out but the folks at
> > electricmotorsport are trying to talk me out of it because they claim that "the
> >
> > brushes will tarnish in the water". Has anyone had this problem? Has anyone
> >used
> >
> > the ME0909? Thanks. Bruce
> >
>
>
>
>
> ------------------------------------
>
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>
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