Catalac Breast Question

[KnightSail]

Good day all.

Have a Catalac 12M/41'. On the breast there are 2 drain holes where the center deck locker drains out. When on a long sail both of the (plastic?) clam shells broke off. These clam shells were about 4" x 4". Both were screwed in place and epoxied along the edges. There are 2 more of these clam shells on either of the P & S hulls for the P & S bow lockers. They are still in place and were installed using the same method.


The original clam shells have not been able to be sourced so different ones of varying sizes and materials have been used to replace. SS, plastic and more recently PVC pipe cut epoxied (and painted to protect from UV), and finally a piece of 3mm EPDM. All of these attempts have failed on the port drain hole cover. The PVC pipe piece has survived the hostile conditions that occur under here ON THE STBD drain hole.



The conditions under there are quite violent which results in waves crashing forward after hitting the breast. What has happened that is the cause of this query is that when the above materials have been used, the deck's gel coat had become compromised when some of the screws were pulled out when the waves removed the clam shells. There are also significant (4-6' long) spider cracks in the gel coat along the inner corners of the forward/aft ribs as this breast flexes with the impact with the waves.



Several Cabosil/Silica thickened epoxy and fiberglass patches have been done over the area as some cracks in the surface have appeared in the fiberglass below the gel coat. The hope was to strengthen this area to keep these cracks from growing. The most recent attempt was to use a piece of EPDM (3mm rectangular, screwed in the corners with an adhesive applied where the screws go into the breast). The hope was that using a flexible product, it would stay in place and not cause damage if it also got torn off. Recently this piece did in fact get torn but one screw held it from falling off. All 4 screws survived in the breast. On closer inspection there are new cracks around the perimeter of the last epoxy/glass repair job.


Now the question (thank you for your patience): Does anyone have any experience with a viable solution for replacing the clam shell in this area that won't result in damage to the breast, please?


Thank you for your time and hopeful solution / response.

[SailingHarmonie]

Although not completely clear, it sounds like these covers are being attached with self-tapping screws into the fiberglass, and the screws are being ripped out. Again making assumptions, I guess that the clamshell is being ripped off by water hitting from the "back side" in the confused waves between the hulls. If this is true, then at least sometimes the clam shell covers are not keeping water OUT rather they are scooping it IN. Maybe you will in the end result be better off without the covers altogether?

But assuming that you feel the covers serve a useful purpose...

It seems to me that the cause has absolutely nothing to do with the materials of construction of the cover, but rather its method of attachment, and the answer is clear. Ditch the screws, and use bolts through the hull to nuts on backing plates (preferred) or large washers on the inner surface.

Alternatively, use something as a form and glass over it with a wide base to the surrounding hull. That makes the cover an integral part of the hull, and has the added advantage that it covers the damage that has already been done. It is of course not removable, but is that important?

[Chotu]

i had this boat and agree with sailingharmonie

mine fell off too and were never replaced. they were unnecessary.

[Tupaia]

Originally Posted by SailingHarmonie

Although not completely clear, it sounds like these covers are being attached with self-tapping screws into the fiberglass, and the screws are being ripped out. Again making assumptions, I guess that the clamshell is being ripped off by water hitting from the "back side" in the confused waves between the hulls. If this is true, then at least sometimes the clam shell covers are not keeping water OUT rather they are scooping it IN. Maybe you will in the end result be better off without the covers altogether?

But assuming that you feel the covers serve a useful purpose...

It seems to me that the cause has absolutely nothing to do with the materials of construction of the cover, but rather its method of attachment, and the answer is clear. Ditch the screws, and use bolts through the hull to nuts on backing plates (preferred) or large washers on the inner surface.

Alternatively, use something as a form and glass over it with a wide base to the surrounding hull. That makes the cover an integral part of the hull, and has the added advantage that it covers the damage that has already been done. It is of course not removable, but is that important?

Would agree with this, but assuming their actual purpose is as drains what about fitting flush scupper valves. These would not get ripped off but still provide for drainage.

[KnightSail]

Thank you SailingHarmonie,


Not self-tapping but SS pan head screws were used for the clam shells and EPDM.


Not all screws were ripped out. Maybe 50% over the various attempts.


It's believed that the wave action is coming from the front initially but then blasted in the opposite direction by the shape of the hull.


We would like to keep the clam shells in order to prevent sea water from "geysering" up into the chain locker.


The concern with using bolts is that since the area flexes with the impacts, that the bolts may egg out the holes they are drilled into over time. Thank you for the suggestion that has not (yet?) been tried.



Please see the photo attached. This is the original clam shell that is still on the vertical hull and the PVC cover that is still in place on the stbd side locker drain hole.



When attaching the PVC piece it was not "glassed in" but both cabosil thickened epoxy was applied over a P-37 product that does adhere to PVC. Perhaps laying a long strip of fiberglass (forward and aft) over the same type of PVC piece would give more surface area for the needed adhesion?


We are not concerned about removing it at the present time.

[KnightSail]

A drag and drop photo was shown on the draft response but isn't showing in this forum?

[KnightSail]

Thank you Tupaia,


Am familiar with that product. Have installed 3 in the past. The rubber flap would certainly get torn off.

[SailingHarmonie]

Originally Posted by KnightSail

The concern with using bolts is that since the area flexes with the impacts, that the bolts may egg out the holes they are drilled into over time. Thank you for the suggestion that has not (yet?) been tried.

If the area flexes that much with wave impacts, then a properly executed backing plate would be a very useful addition. If it is that bad, maybe the addition of a stringer to stiffen the whole panel? Bending fiberglass enough does--eventually--cause it to fail.

If the water is ripping these off through hitting them from behind, you already have more severe "geysering" into the locker than you would have without any cover on them at all.

[KnightSail]

SailingHarmonie,


Correction: Yes, self tapping screws were used.
Thank-you for your response.