Moving sterndrives

[Peterjfinch]

Tony, The existing cutouts are 33" centres. the new engines are 33 3/4" wide. So, in my mind, the new cutouts must have a centre of about 35 3/4"-

Please tell me I´m wrong.

Pete

[Tony Davis]

Forget about centres for the moment, I'm asking how much bigger is the cutout (hole) for the TRS compared to the Alpha?

[Peterjfinch]

Just been out and measured the hole. The Alpha hole is 7 1/4" wide, max. The TRS is about the same width but longer.

Pete

[Tony Davis]

Oh dear, what you like at fibreglassing?

[Peterjfinch]

I guess I must learn! Just wanted to know how much I have to do....The entire transom or just add a splice to the side of the mounting hole?

[Peterjfinch]

I guess chewing gum and sawdust, is out of the question?

[larby]

Ha ha. Just to chip in here, to me your best bet would be to glass up the existing holes completely, no need to do the whole transom, then recut as though it were a new boat to the exact spec you want.

It's not a tricky job, but one that needs to be done in quite a specific way to ensure the plugs don't just pop out! I'll have a look and see if I can find something that explains how to do it, or TD could quite possibly describe it?
It's something I'venever yet had to do, but for some reason I made a point of learning how!
Hope you don't mind itching!!

James

[scarab racing]

Hi Peter
I'm no expert but I agree with glassing up the holes, then recutting were you want / need them. It is quite easy to fill in the holes and re drill /cut just take your time and plod slowly.
The way I glassed my twin engine to single was to screw a flat piece of formica or similar to the transom (outside) then work on filling it in from the inside that way any overspill or messups are all inside and won't be seen or can be sorted easier, also the out side should then be easier to sort as should be almost flat and finished when you remove the formica/perspex.
Pic attached of mine. not bad for a diy.

[Tony Davis]

Originally Posted by Peterjfinch

I guess chewing gum and sawdust, is out of the question?

Hmm, the worry will be that that that is what you find. I'm just finishing up a job that was supposed to be just filling the cutouts on a twin engine boat, but ended up being a complete transom replacement due to rot.

The glass was obviously fine, but it entailed complete removal of all transom timber, plus removing some of the longits so as to be able to put the new ply in.

It some respects it probably made it an easier job, but more time consuming and expensive.

[biffer]

if you're going down the route of glassing in then you should know how your transom was layed up, from the outside working in there should be, 2 gell coats, a few layers of mat, one 18mm ply, more matt another ply and then more matt.
cut from the inside about 75mm all around the drive cutouts, go carefull and leave the outer grp face intacted, (more about that later), start again from the inside and cut a further 75mm but only go to the first layer of ply, from the inside grind back the original grp to clean up the face of the last ply
you should by now have stepped rings leading away from your drive hole.
back to your grp face, feather that back with a grinder to make the edge of your original cutout sharp (you will see as you grind the original layers of matt in rings), Now you're ready to start putiing back

cover the outside holes with conti board (shiney chipboard), everything else is from the inside, 2 layers of gell to the conti board right to the sharp edge of you're original gell, let that dry, then there should be about 2x600grams and a 800/300 combi matt in there and then a ply cut ot the exact size of you're first cutout, wedge that in and let it dry, when dry lay in about 3x600grams matt and the last ply, wedge and leave to dry, last job is to glass over the lot, if when cutting out the last ply the 2 holes overlap put one big ply in instead.
remove the shiney board from the outside and you should only have a flash line to rub down
i hope this make some sense, pm me and i'll give you a contact number, good luck, biff

[Charlie Hunter]

Wow tony, that looks like one nightmare of a job!!

I totally agree that glassing up the transom and starting again is the way forward. I am not skilled at all with fibreglass however I can recognise if a job is being done correctly or not. In the case of glassing up transom holes prior to re-cutting I personally would only use an expert. Consider the enormous forces acting upon the transom via the drives. I watched my guy glass up a simple exhaust hole and it involved splicing marine ply, epoxy glues/resins, tri/quad axial woven rovings (looks like the stuff seat belts are made of), additional heat etc etc. Performing these types of structural glass jobs correctly is quite involved and skillful and I would be terrified at the prospect of half the transom falling out. Thats just my opinion

[Peterjfinch]

Originally Posted by larby

Ha ha. Just to chip in here, to me your best bet would be to glass up the existing holes completely, no need to do the whole transom, then recut as though it were a new boat to the exact spec you want.

It's not a tricky job, but one that needs to be done in quite a specific way to ensure the plugs don't just pop out! I'll have a look and see if I can find something that explains how to do it, or TD could quite possibly describe it?
It's something I'venever yet had to do, but for some reason I made a point of learning how!
Hope you don't mind itching!!

James

hi James, Thanks for your input, always welcome. There are different views but it´s looking like, as you say, that could be the way forward. Biffer´s description sounds like what I was thinking of. the only part I thought differently, was, after putting both the pieces of ply in and letting them set quite well, then to grind out the outer glass and re glass outside, getting wider every layer. Not sure if this is correct but sure does feel stronger, from the outside.

Anything you find would be great to read, thanks.

"Itching"? I´m itching to get this done and see those engines pumping salt water out the exhausts.

Pete

[Peterjfinch]

Originally Posted by biffer

if you're going down the route of glassing in then you should know how your transom was layed up, from the outside working in there should be, 2 gell coats, a few layers of mat, one 18mm ply, more matt another ply and then more matt.
cut from the inside about 75mm all around the drive cutouts, go carefull and leave the outer grp face intacted, (more about that later), start again from the inside and cut a further 75mm but only go to the first layer of ply, from the inside grind back the original grp to clean up the face of the last ply
you should by now have stepped rings leading away from your drive hole.
back to your grp face, feather that back with a grinder to make the edge of your original cutout sharp (you will see as you grind the original layers of matt in rings), Now you're ready to start putiing back

cover the outside holes with conti board (shiney chipboard), everything else is from the inside, 2 layers of gell to the conti board right to the sharp edge of you're original gell, let that dry, then there should be about 2x600grams and a 800/300 combi matt in there and then a ply cut ot the exact size of you're first cutout, wedge that in and let it dry, when dry lay in about 3x600grams matt and the last ply, wedge and leave to dry, last job is to glass over the lot, if when cutting out the last ply the 2 holes overlap put one big ply in instead.
remove the shiney board from the outside and you should only have a flash line to rub down
i hope this make some sense, pm me and i'll give you a contact number, good luck, biff

Hi biff, Thanks for that, very detailed and what I was thinking of. Would it be stronger if the outer glass was ground outwards, from the outside, and then glassed outside?

Thanks again.

Pete

[Peterjfinch]

Originally Posted by Charlie Hunter

Wow tony, that looks like one nightmare of a job!!

I totally agree that glassing up the transom and starting again is the way forward. I am not skilled at all with fibreglass however I can recognise if a job is being done correctly or not. In the case of glassing up transom holes prior to re-cutting I personally would only use an expert. Consider the enormous forces acting upon the transom via the drives. I watched my guy glass up a simple exhaust hole and it involved splicing marine ply, epoxy glues/resins, tri/quad axial woven rovings (looks like the stuff seat belts are made of), additional heat etc etc. Performing these types of structural glass jobs correctly is quite involved and skillful and I would be terrified at the prospect of half the transom falling out. Thats just my opinion

Hi Charlie, Point taken. I do agree with you, if there´s anything wrong with the transom wood. I´m just not that sure that it would be any safer, than doing a propper job with the existing holes. To weaken the entire transom feels a little over the top, but again, I don´t know enough to make a qualified decision on this and want to hear from "the guys who know".

Thanks for making the point.

Pete

[Peterjfinch]

Originally Posted by scarab racing

Hi Peter
I'm no expert but I agree with glassing up the holes, then recutting were you want / need them. It is quite easy to fill in the holes and re drill /cut just take your time and plod slowly.
The way I glassed my twin engine to single was to screw a flat piece of formica or similar to the transom (outside) then work on filling it in from the inside that way any overspill or messups are all inside and won't be seen or can be sorted easier, also the out side should then be easier to sort as should be almost flat and finished when you remove the formica/perspex.
Pic attached of mine. not bad for a diy.
Attachment 28650

Hi Scarab, For someone who is not an expert, that job looks good to me. I think you are right with this way, I only ask if it would be better to grind and glass from the ply to the outside, from the outside? Thinking of extra strength. I know it will make it harder to get it flat later but it´s the strength that I was thinking about.

Thanks again.

Pete

[Peterjfinch]

Looks like there are "For´s" and "Against" on this subject.

I would guess that if I follow the "Plug" idea, any bad wood would become apparent quite soon. Then a complete transom is the only answer.

Would my boat benefit from a centre stringer? if yes, how far forward would it have to go and what size would be best? I am thinking of removing all the pretty wooden flooring, in the engine bay. I don´t know what´s under it and it would lose some weight also. Is this a good idea?

I have noticed the picture below. Can anyone explain all the shapes that can be seen, i.e. why does it have the cross pieces between the stringers and are those kind of mounts OK. If yes, what are they made from? Would they suit my project?

Any ideas welcome

Thanks

Pete

[biffer]

i've always started from the inside, if you find any bad wood etc you haven't destroyed the outside shape, you can dig around all you like on the inside, the outside is harder to get right again, i've done quite a few this way and touch wood they 're still going strong

[Peterjfinch]

I understand about working from the inside. I was just thinking that, if I rout out the steps and put the ply in, then finish the glass inside. I could then grind out the outside fibreglass and re glass that, from the centre out. Wouldn´t this make the joint stronger and create more support for forward forces?

I am only thinking out loud and I have no expertise in this field.

Pete

[Peterjfinch]

Forgot to add photo for previous post.

[Tony Davis]

Originally Posted by Peterjfinch

I understand about working from the inside. I was just thinking that, if I rout out the steps and put the ply in, then finish the glass inside. I could then grind out the outside fibreglass and re glass that, from the centre out. Wouldn´t this make the joint stronger and create more support for forward forces?

I am only thinking out loud and I have no expertise in this field.

Pete

That's the way I always do it.