Filling in transom holes from sterndrives.

[Steve13]

Hi, Looking at some pointers in filling in my transom holes.

I am replacing the old twin sterndrives and engines with a new engine - long story but well committed now.

The old “holes” need to be filled and a new centre “hole” cut. I have removed the inner core and made a new core from 2 x 18mm Marine Ply all bonded together with thickened epoxy and is ready to be bonded to the outer skin.

I have 3 questions.

1. Should I bond the new core in place first? Advantages are that I can see that the new core is flush tight against the outer skin. I can use the old sterndrive mounting holes to brace the inner core tight against the outer skin together with a number of through additional bolts across the core. I can use the “bonded” core as a blanking plate to finish off the outside.

2. Alternately, should I fill the holes first, make good and flush on the outside and using a temporary blanking plate on the inside. Advantage is that the new core will have “presumably” a better and stronger bond? The filling of the holes will be variety of CSM and triaxial cloths and using vinylester resin as this is compatible with the original boat layup. Then gelcoat.

3. The outer skin is 10mm thick. Using the bevelling 12:1 ratio I just do not have the width at the top and bottom for 120mm. At the top I have 75mm and the bottom I have a minimum in one place of 60mm. Width is all fine and at a 45degree angle at the bottom I have 100mm. Please see image. Is there an alternative way round that or am I worried unnecessarily? The inside of the skin has been prepared and perfectly flat and the new core will be tabbed in place after bonding.

Appreciate any guidance.

 

[Blueknarr]

Welcome to the forum.

I would bond in the new core first. No need for a temporary former.

I've seen bond zone bevel ratios as low as 8/1. So I would take the repair zone as close to the top and bottom as possible. Then not worry about it.

Good luck

 

[Steve13]

Welcome to the forum.

I would bond in the new core first. No need for a temporary former.

I've seen bond zone bevel ratios as low as 8/1. So I would take the repair zone as close to the top and bottom as possible. Then not worry about it.

Good luck


Many thanks for your welcome and response, it is much appreciated.

I have to admit my preferred option is to bond in the new core first as I can easily see if the core is flush tight against the outer skin with no voids and smooth off the thickened resin from the holes.

 

[Tops]

I am of the school of largest pieces of cloth first when covering the new core to the existing beveled outer transom.
Welcome to the forum and all the best on repairs and repowering.

 

[wet feet]

For that situation,just do the best you can.I'm of the persuasion that increases the size of successive pieces of glass as the job progresses.What I do recommend is using a piece of melamine faced chipboard as a surface to mould on and temporarily locating it securely on the outside surface.Obviously it needs to be waxed for release purposes and after waxing handle with care and DON'T touch the bonding surface before you have cleaned any wax off your hands or discarded the gloves you wore.Gel on the new surface and then add the first plies of mat.Then bond in your core,but with no sterndrives you might not need such a thick piece except for appearance's sake.You can bond the core as well as possible then add the inner laminates before stripping away the melamine faced board on the outside and dealing with any cosmetic issues.There shouldn't be too many of those if you take the time to set the job up accurately and it takes less time to prepare well than to do a big cosmetic job.

 

[fallguy]

Hi, Looking at some pointers in filling in my transom holes.

I am replacing the old twin sterndrives and engines with a new engine - long story but well committed now.

The old “holes” need to be filled and a new centre “hole” cut. I have removed the inner core and made a new core from 2 x 18mm Marine Ply all bonded together with thickened epoxy and is ready to be bonded to the outer skin.

I have 3 questions.

1. Should I bond the new core in place first? Advantages are that I can see that the new core is flush tight against the outer skin. I can use the old sterndrive mounting holes to brace the inner core tight against the outer skin together with a number of through additional bolts across the core. I can use the “bonded” core as a blanking plate to finish off the ..

2. Alternately, should I fill the holes first, make good and flush on the outside and using a temporary blanking plate on the inside. Advantage is that the new core will have “presumably” a better and stronger bond? The filling of the holes will be variety of CSM and triaxial cloths and using vinylester resin as this is compatible with the original boat layup. Then gelcoat.

3. The outer skin is 10mm thick. Using the bevelling 12:1 ratio I just do not have the width at the top and bottom for 120mm. At the top I have 75mm and the bottom I have a minimum in one place of 60mm. Width is all fine and at a 45degree angle at the bottom I have 100mm. Please see image. Is there an alternative way round that or am I worried unnecessarily? The inside of the skin has been prepared and perfectly flat and the new core will be tabbed in place after bonding.

Appreciate any guidance.

Install core first. Precoat plywood as it likes to suck resins. Bond the edges lightly. Use shipping tape over a spacer to allow for the glass margins. So, you’ll have an mdf backer with a spacer and ship tape over it. The spacer fits inside the keyhole. After the core is in place; you can fill the margins better from each side after removing the former. The other way sucks, too much room for poor lamination.

 

[Steve13]

Install core first. Precoat plywood as it likes to suck resins. Bond the edges lightly. Use shipping tape over a spacer to allow for the glass margins. So, you’ll have an mdf backer with a spacer and ship tape over it. The spacer fits inside the keyhole. After the core is in place; you can fill the margins better from each side after removing the former. The other way sucks, too much room for poor lamination.

Thank you – pretty much what I intended. I have pre-coated the core with 3 coats of resin, the first 2 “thinned” with a little styrene (first 6% the second 2%) for absorption.

 

[fallguy]

Thank you – pretty much what I intended. I have pre-coated the core with 3 coats of resin, the first 2 “thinned” with a little styrene (first 6% the second 2%) for absorption.

Sand it for mechanical key a bit..

 

[Dillusion]

I just filled mine in and I hope it holds as well.

I bonded all my core ply together first. (2) 3/4" (1) 1/4". I also left the stainless screws that was holding the pieces together in the core.
Placed a sheet of ply on the outside of the transom covering the openings. I put paint mixing sticks between the ply and my core to leave some gap. Glass the inside. Removed the outside ply and mixing sticks and glassed the outside.

I also did not have room for the correct ratio at the bottom of my transom I just went as far down as I could. Ended up with (5) layers of 1708 inside and outside.

19 Glasply I/O to Outboard https://www.boatdesign.net/threads/19-glasply-i-o-to-outboard.68834/