[sailingdog]

Originally Posted by mikehoyt

A number of years ago I purchased a Raymarine ST40 Bi-Date Speed/depth/log instrument that comes with two thru-hull transducers.

Due to the layout of the inside with a shallow bilge and the intake and outflow thru hulls for the head that had been installed forward I installed these thru hulls port and stb beneath port & stbd settees as close to centerline as possible beneath these settees. The problem is that when the boat heels more than say 15 degrees either the speed or depth transducer stops working.

The diagram below illustrates the bottom of my hull and shows approximately where the existing thruhulls for the marine head and the transducers are located and where I can move them. The locations available are limited by a depth beneath the floorboard of less than three inches between settes and in head area. Where I have indicated is under the vee berth behind the water tank whereas the head thru hulls are fwd of the water tank.

diagram at http://fulltilt2pics.angelfire.com/thruhulls.GIF

The transducers are sealed with 3M 4200 I believe.

The image isn't there. This is what I see when I click on it:

My plan is to remove them and then fill the holes using West or East system epoxy grinding a tab angle both inside and outside the hull.

Grind to an 8:1 bevel or thereabouts if possible.

I would start by placing plastic wraop on the outside of hull held in place with tape. Then I woudl move inside and put a layer of cloth just larger than the hole in place, followed by glass matt the sise of the hole followed by glass cloth increasing in diameter (2 layers) over the matt. I would then saturate with resin (I would use fast hardener) and then move to the hole on the other side and repeat.

After a suitable time period (maybe an hour?) I would go outside, remove the plastic wrap and apply two - three layers of cloth and resin on each hole. Not sure how to stop it from dripping but suspect plastic wrap and tape could be used to hold in place.

Repeating this process of alternating between inside and outside I would build up the patch to the thickness of surrounding hull. Then wait 24 hours to cure and apply thickened epoxy witha sandable filler (probably west 407) to build up to a smooth surface - sanding with 80 grit and Random orbital sander. Also inside.

I would use at least three or four layers on the inside, and the same on the outside. Don't over saturate the cloth... just wet it out enough so that it turns transparent... laminates are stronger and lighter if they have a higher ratio of glass to resin—as resin itself is fairly weak and heavy. Get rid of the air in the laminate as well. Good fiberglassing should appear almost transparent...it is glass after all. If it is whitish or cloudy...it still has a lot of air trapped in it. After it cures, it should have a nice greenish translucent appearance.

Also, if you're using West System... don't forget to scrub the cured laminate with a scotchbrite pad and rinse heavily with water... If you don't the amine blush will prevent the thickened epoxy filler from bonding properly. Don't use microballon filler, use chopped glass strand instead. The microballon fillers will absorb water—chopped glass won't.

Any comments on transducer locations? Will the flow over fwd head thru hulls affect in any meaningful way?

Turbulence may affect the depth transducer's ability to function properly. Most depth transducers are recommend to be installed aft of center.

What does epoxy need to be overcoated with before applying bottom coat (Micron CSC)? Inside I would use a primer and then a bilge paint.

Don't forget to scotchbrite scrub and rinse the epoxy to remove the amine blush, then sand to roughen the surface a bit. Use Interprotect 2000E as a primer, then paint with your bottom paint.