thesaintlyone
Well-Known Member
On a semi related thread to my other post what would be the approximate cost to fill in two transom drive holes and cut a new transom drive hole for a single engine install. Both DIY and Hiring a professional.
Cost to fill in two transom outdrive holes and cut single drive hole
- Thread starter thesaintlyone
- Start date
kashurst
Well-Known Member
I have a vague memory from Motorboats Monthly going back decades, someone did this. They cut the new hole in the centre. Then I think they covered the transom with a large and suitably thick, piece of marine ply. (could have been a series of layers, glued together) Fibre-glassed it all to protect it, then cut a new hole in the new ply transom . DIY wise probably quite cheap and easy. Does this ring any bells with anyone else?
I suspect if you just fill the two old holes and then cut a new hole in the middle your transom will not be strong enough.
I suspect if you just fill the two old holes and then cut a new hole in the middle your transom will not be strong enough.
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burgundyben
Well-Known Member
Forumite Le Scarron did exactly this.
Dill et Bound
Well-Known Member
The remodeling of the transom is really the easy bit.
The main problem with any project of this type is to incorporation of the new engine beds into the structure
Very often the new engine beds will align with the holes in the transom of the twin installation.
This requires a little bit of working out.
To get over this I have in the past removed a large amount of the plywood stiffening in the transom beyond the outer engine bed of the twin installation . Cut down the inner engine beds. Re laminated the 2 holes. Rebuilt the layers of ply , and incorporated the new wooden or metal engine beds into the structure before relaminating the whole transom incorporating the new beds into that layup.
The cutting of the new hole to allign with the new engine beds is then far more accurate.
So...
Unless you are confident I would seek the services of a competent boatbuilder with the facilities to undertake the work.
It’s probably going to be quite expensive but having it done to a high standard will be worth every penny, as this good preparation will ease the installation costs, which you may be able to do yourself
It will also satisfy any surveyor that may look at the boat at a later date as part of a sale process.
,
The main problem with any project of this type is to incorporation of the new engine beds into the structure
Very often the new engine beds will align with the holes in the transom of the twin installation.
This requires a little bit of working out.
To get over this I have in the past removed a large amount of the plywood stiffening in the transom beyond the outer engine bed of the twin installation . Cut down the inner engine beds. Re laminated the 2 holes. Rebuilt the layers of ply , and incorporated the new wooden or metal engine beds into the structure before relaminating the whole transom incorporating the new beds into that layup.
The cutting of the new hole to allign with the new engine beds is then far more accurate.
So...
Unless you are confident I would seek the services of a competent boatbuilder with the facilities to undertake the work.
It’s probably going to be quite expensive but having it done to a high standard will be worth every penny, as this good preparation will ease the installation costs, which you may be able to do yourself
It will also satisfy any surveyor that may look at the boat at a later date as part of a sale process.
,
MapisM
Well-Known Member
Do yourself a favour and don't do that, regardless of costs.
Dill et Bound
Well-Known Member
Costs are really important of course but.
You buy a petrol engined nice boat for say 20k
Spend perhaps 5k on it in canopies new upholstery etc.
You drop a valve and write off an engine.
The engine removed reveals corrosion in the shield and exhaust horn.
Bad news is the other shield has similar issues.
How much is your 25k investment now.
Replacement of the 2 engines and drives are an eye watering 18k plus.
A single reconditioned deisel with drive becomes available for 9k
The sums to convert to new single engine come in at perhaps 4K
At this stage you look to the future.
The single option will give greater economy and possibly a higher resale value.
The twin replacement will give you back more or less exactly what you had but at an investment of over 40k.
Maybe a few knots off top speed..
It’s a problem with all powered boats.
It really is all about the cost.
Investing in a boat of any kind is going to be a bit expensive.
Bouba
Well-Known Member
I’d cut the new hole very carefully and then use it as a plug to fill one of the other holes
thesaintlyone
Well-Known Member
My ultimate hope would be to install a single diesel Volvo D3 225 or similar nice clean and efficient
Dill et Bound
Well-Known Member
That sounds like a great project.
And as far as using the cut out to fill one of the holes is concerned.
I would tend to avoid it.
The fact is that what ever you decide to do as far as re engineering you project.
It needs to be done in a way that increases the value of the boat.
By Sikaflexing a bit of boat into a hole you may on a nice day out you many have a bit more to worry about than Brexit..
Beamishken
Well-Known Member
Personally I'd probably start by cutting the hole for the new drive first then id remove the inner transom glass across the width of the 3 holes probably as far as the outer stringers and the origional ply & replace with fresh layers of ply sandwiched and glassed into place. probably need to reduce or remove the original inner engine mounts and fabricate new ones butted up to the new transom structure. The drive cut out position is fixed, the engine mounts are fabricated to accommodate the drive and angle of the transom everything is determined from the crankshaft centreline and mount heights are worked from there. Most engine manufacturers give dimentions of a jig to set the engine mounts up from the transom shield hence my reasoning the hole should be cut first.
Once the new plywood transom is bonded into place the old holes should be ground back to a taper and glass built up to thickness then faired and gelcoated.
I wouldnt just fill the holes in the transom imho thats asking for trouble
Estimate on material costs would be £3-500 for a good diy job
Once the new plywood transom is bonded into place the old holes should be ground back to a taper and glass built up to thickness then faired and gelcoated.
I wouldnt just fill the holes in the transom imho thats asking for trouble
Estimate on material costs would be £3-500 for a good diy job
Bouba
Well-Known Member
I would measure everything very carefully first. The new transom hole will probably sit lower than the two old ones. Meaning the engine will have to sit lower but if it’s a taller engine then you may not be able to fit it low enough
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Personally I would fill all the holes first and then treat the transom as new with a new single installation. Depending on the size of the engine it won't be on centre due to prop walk.
I did this on a RIB that had twin 75hp engines that were replaced with a single 140. Holes were filled with laminated up plugs made using marine ply and Gurit epoxy / colloidal silica etc. The transom was probably stronger than when new.
I did this on a RIB that had twin 75hp engines that were replaced with a single 140. Holes were filled with laminated up plugs made using marine ply and Gurit epoxy / colloidal silica etc. The transom was probably stronger than when new.
Dill et Bound
Well-Known Member
I think you can forget the offset as most duo. Props take that out the equasion.
BMW power in Avengers had 4 inches but they produced huge torque and they were very deep V.
I think that cutting the hole before making the new stiffened transom an integral part of the boat isn’t a good idea.
I think that the amount of work internally on the beds to change from single to twin, the height of the engine,and also the trimmed up drive position that will determine the height of those beds need to be established at an early stage. Which would point to the final hole being positioned later.
I would also look at a slight splay off centerline perhaps 1 ft behind the front engine mounts to give better access to the exhaust horn and rear of the engine.
It also forces any. Spray picked up from the vents or water from anywhere else to flow forward where it can be picked up easily from in front of the engine.
But as I said in an earlier post.
I would entrust the work to an experienced tradesman who would foresee all the potential problems, and work out a plan that will give you a solid structure to fit the new power plant.
And hopefully many years of fun on the water, and good resale potential.
BMW power in Avengers had 4 inches but they produced huge torque and they were very deep V.
I think that cutting the hole before making the new stiffened transom an integral part of the boat isn’t a good idea.
I think that the amount of work internally on the beds to change from single to twin, the height of the engine,and also the trimmed up drive position that will determine the height of those beds need to be established at an early stage. Which would point to the final hole being positioned later.
I would also look at a slight splay off centerline perhaps 1 ft behind the front engine mounts to give better access to the exhaust horn and rear of the engine.
It also forces any. Spray picked up from the vents or water from anywhere else to flow forward where it can be picked up easily from in front of the engine.
But as I said in an earlier post.
I would entrust the work to an experienced tradesman who would foresee all the potential problems, and work out a plan that will give you a solid structure to fit the new power plant.
And hopefully many years of fun on the water, and good resale potential.
Beamishken
Well-Known Member
When installing an engine the height of the engine is determined by the keel line. it is prety much set in stone within a very small margin depending on transom angle. Mercruiser produce a template to affix to the transom for this purpose volvo probably the same. Everything is referanced from the transom shield after it is installed. Fitting engine mounts before fitting the transom shield is pure guesswork there is nothing inside the hull to reference off to build engine mounts until the shield is trial fitted. Hence the suggestion the hole be cut early in the process. The hole also gives access to install numerous clamps to hold the new ply being glassed in
Dill et Bound
Well-Known Member
Ok...
I do see your point about clamping the ply in position.
But from my experience it’s far easier to make good the gel and all the glassing to the outer skin of the boat before you cut another massive hole in it.
I have always used a template to get the engine mounted in the right place.
And never had any real problems in fitting engines from the manufacturers spec.
But every job produces a new set of challenges I suppose.
I do see your point about clamping the ply in position.
But from my experience it’s far easier to make good the gel and all the glassing to the outer skin of the boat before you cut another massive hole in it.
I have always used a template to get the engine mounted in the right place.
And never had any real problems in fitting engines from the manufacturers spec.
But every job produces a new set of challenges I suppose.