Change from Outdrives to Twin Shafts and Props

[Nike55]

Have inherited a 31 ft fibreglass hull (poss 'Project' or 'Island Plastics') with no drives or engines.

Have located 2 Volvo petrol 6 cyl B30's which should fit but no luck with locating Volvo AQ270 outdrives and shields.

Thinking of converting to shafts and props (will need appropriate gearboxes etc!)

Anyone in the UK (South East) know any engineers who can advise on drilling holes in hull and blocking up transom apertures?

 

[ChromeDome]

History has it that outdrives in general and B30's in particular means a lot of hard earned used to pay for experiences that you'd rather be without.

Conversion to shafts isn't straightforward but if your planned/intended use allows, a bracket and outboard(s) is an easier & faster way to go.



Do a full and comprehensive budget before you even start - without optimistic assumptions.
Boaty things are complex and expensive.

 

[Momac]

Will this change need a fresh RCD certification ?

 

[penfold]

Have inherited a 31 ft fibreglass hull (poss 'Project' or 'Island Plastics') with no drives or engines.

Have located 2 Volvo petrol 6 cyl B30's which should fit but no luck with locating Volvo AQ270 outdrives and shields.

Thinking of converting to shafts and props (will need appropriate gearboxes etc!)

Anyone in the UK (South East) know any engineers who can advise on drilling holes in hull and blocking up transom apertures?

you need a laminator, not an engineer, for blocking up outdrive holes.

History has it that outdrives in general and B30's in particular means a lot of hard earned used to pay for experiences that you'd rather be without.

Conversion to shafts isn't straightforward but if your planned/intended use allows, a bracket and outboard(s) is an easier & faster way to go.
View attachment 161939


Do a full and comprehensive budget before you even start - without optimistic assumptions.
Boaty things are complex and expensive.

That's pragmatic advice, although proper O/B installs are hardly less work than fitting inboards if the hull is not already shaped for it.

 

[Nike55]

you need a laminator, not an engineer, for blocking up outdrive holes.

That's pragmatic advice, although proper O/B installs are hardly less work than fitting inboards if the hull is not already shaped for it.

History has it that outdrives in general and B30's in particular means a lot of hard earned used to pay for experiences that you'd rather be without.

Conversion to shafts isn't straightforward but if your planned/intended use allows, a bracket and outboard(s) is an easier & faster way to go.
View attachment 161939


Do a full and comprehensive budget before you even start - without optimistic assumptions.
Boaty things are complex and expensive.

History has it that outdrives in general and B30's in particular means a lot of hard earned used to pay for experiences that you'd rather be without.

Conversion to shafts isn't straightforward but if your planned/intended use allows, a bracket and outboard(s) is an easier & faster way to go.
View attachment 161939


Do a full and comprehensive budget before you even start - without optimistic assumptions.
Boaty things are complex and expensive.

I'm happy rebuilding the B30's but if too far gone I'll buy alternative engines (petrol)

The boat weighs 4 tons and has semi displacement hull - a couple of outboards won't quite work for me

The budget is £20k - the boat won't be worth even half that in the end but that's not what its about - its a retirement vanity project.

 

[Bajansailor]

Have inherited a 31 ft fibreglass hull (poss 'Project' or 'Island Plastics') with no drives or engines.

Can you post some photos please of the hull that you have inherited, including photos of the engine compartment?

 

[ChromeDome]

Twin engines + tubes & shafts + gearboxes + reinforcement of hull + brackets + rudders/hydraulics + rebuild of engine bay/mounts + cables and more. A lot to spend time on


It's an exciting project, hard to judge if the budget is sufficient without knowing the boat and your expectations for the result. Or your schedule.
Pictures would be great.

31' Semi-planing and with 2x170 hp sounds a bit unusual. How do you intend to use the boat?

Volvo's B30 was made from 1968 to 1975 (a fairly short production run) and was basically a cast iron 4-cylinder B20 with two extra cylinders. Made in 117-175 hp versions, the marine version was marketed by Penta with 3 downdraft carburettors and a hotter camshaft to make 170 flywheel hp. Known to consume a lot of fuel.
Not many were fresh water cooled and most have long since rusted away.

Modern 4-strokes are in many ways better (and use far less petrol) than old car engines that were marinised, and spare parts for marine B30s are difficult or impossible to find.


I wouldn't rule out outboards completely. They are complete units with engine, gearbox, shaft, propellers, steering and all. Good access to service and maintenance and easy to replace should the need arise.
In addition, they solve the safety issue when petrol engines are in a closed space inside the boat.

 

[colhel]

If you're converting to shafts, the engine may have to be moved forward quite considerably.

 

[simonfraser]

lots of this about on youtube, the pod can be made big enough to provide xtra floation aft if needed

 

[PCUK]

Great to hear that you are doing the job just because you want to! I've done that all through my boating "career". Personally I would keep looking for drives as this will be a much easier project. Don't fixate on any particular make or model, just find a pair that will do the job. Don't involve professional outsiders in the project as that will make it too costly. Everything you need to know/learn is available in books and on You-Tube which is a fantastic resource in finding out how to do things! You will have a comprehensive set of 'experts' here with varying degrees of expertise, just sort out the wheat from the chaff! As a new member you will probably not be able to post pics until you have made a few posts. Once you can get some pictures up the advice will be more targeted and accurate. If you are a practical type you will love this project. By the way the most important rule of boat rebuilding is to never buy equipment from a boat shop. Always find your local specialist supplier. Hydraulics, stainless steel nuts and bolts, fibreglass, timber, plumbing, electrics, etc. etc.

 

[ChromeDome]

Great to hear that you are doing the job just because you want to! I've done that all through my boating "career". Personally I would keep looking for drives as this will be a much easier project. Don't fixate on any particular make or model, just find a pair that will do the job. Don't involve professional outsiders in the project as that will make it too costly. Everything you need to know/learn is available in books and on You-Tube which is a fantastic resource in finding out how to do things! You will have a comprehensive set of 'experts' here with varying degrees of expertise, just sort out the wheat from the chaff! As a new member you will probably not be able to post pics until you have made a few posts. Once you can get some pictures up the advice will be more targeted and accurate. If you are a practical type you will love this project. By the way the most important rule of boat rebuilding is to never buy equipment from a boat shop. Always find your local specialist supplier. Hydraulics, stainless steel nuts and bolts, fibreglass, timber, plumbing, electrics, etc. etc.

Since Volvo drives have been removed the cut-out in the stern it will fit the same.
Merc drives will need a transom adaptor plate as their cut-out is way smaller

 

[ChromeDome]

lots of this about on youtube, the pod can be made big enough to provide xtra floation aft if needed

Did that once when making a trolling boat out of a 15' hardtop. Added 2' to the length (much needed space inside) and 240 liters/kg buoyancy while carrying a Honda 35. The "bracket" was made of aluminium.

 

[ChromeDome]

If you're converting to shafts, the engine may have to be moved forward quite considerably.

Yes:

 

[Nike55]

Twin engines + tubes & shafts + gearboxes + reinforcement of hull + brackets + rudders/hydraulics + rebuild of engine bay/mounts + cables and more. A lot to spend time on
View attachment 161972

It's an exciting project, hard to judge if the budget is sufficient without knowing the boat and your expectations for the result. Or your schedule.
Pictures would be great.

31' Semi-planing and with 2x170 hp sounds a bit unusual. How do you intend to use the boat?

Volvo's B30 was made from 1968 to 1975 (a fairly short production run) and was basically a cast iron 4-cylinder B20 with two extra cylinders. Made in 117-175 hp versions, the marine version was marketed by Penta with 3 downdraft carburettors and a hotter camshaft to make 170 flywheel hp. Known to consume a lot of fuel.
Not many were fresh water cooled and most have long since rusted away.

Modern 4-strokes are in many ways better (and use far less petrol) than old car engines that were marinised, and spare parts for marine B30s are difficult or impossible to find.


I wouldn't rule out outboards completely. They are complete units with engine, gearbox, shaft, propellers, steering and all. Good access to service and maintenance and easy to replace should the need arise.
In addition, they solve the safety issue when petrol engines are in a closed space inside the boat.

Thanks ChromeDome. Very useful info and in line with my thoughts re tubes / shafts etc.

Will try and post some pics after checking the process on here.

I intend using the boat as an occasional weekender, river cruising with a few estuary / coastal transits - to be honest its more about fixing it up than using it - it's more of a fun learning project than an earnest, determined must-get-it-in-the-water-and- into-the-Med- asap type project. Its a bit like a Series Land Rover project; fun to do up and light use now and again.

Not scared of using petrol; will have blowers and a full check with hatches open prior to start - planning on vibration free fuel mountings as much as possible and automatic engine bay extinguishers, remote fuel shut off. I don't need a lot of range so might opt for smaller baffled and foam filled tanks (similar to racing car types but larger).

If money were no object I would go for twin Detroit diesels and Jacuzzi waterjets - if I could find them at a reasonable price. The 'jets have their own issues but it would be interesting planning the instal!

It does sound a bit unusual but as someone once said: 'Charlie Don't Surf!' (there's a clue).....

 

[Nike55]

Yes:
View attachment 161977

That's taken as read - fortunately it's an open rear cockpit (didn't used to be) so space isn't an issue. If the engines need to be above the deck sole in boxes - no problem.

 

[Nike55]

Did that once when making a trolling boat out of a 15' hardtop. Added 2' to the length (much needed space inside) and 240 liters/kg buoyancy while carrying a Honda 35. The "bracket" was made of aluminium.

View attachment 161976

That is an intriguing idea and one which I had dismissed as I wasn't sure about the stress on the transom and the mounting points, I might revisit this with a marine architect to take account of the stress involved; power outputs / sea states etc.

 

[snowbird30ds]

Where are you planning to use the boat? Dropping twin petrols into a boat that has no engines at all sounds daft to me when diesel is so much safer and easier to get beside the water, would that be a project 31 hull? Although they were generally on outdrives I know of one on the broads that has a single inboard MD32 volvo on a Vee drive so the engine is in "backwards" and the shaft exits at a good angle underneath, made a great broads boat.
If only using on rivers a single outboard on a frame would be the way to go.

 

[PCUK]

My mate had a Senior with the engine amidships on a shaft. Twin Detroits on a river, now that I'd like to see!

 

[Nike55]

Great to hear that you are doing the job just because you want to! I've done that all through my boating "career". Personally I would keep looking for drives as this will be a much easier project. Don't fixate on any particular make or model, just find a pair that will do the job. Don't involve professional outsiders in the project as that will make it too costly. Everything you need to know/learn is available in books and on You-Tube which is a fantastic resource in finding out how to do things! You will have a comprehensive set of 'experts' here with varying degrees of expertise, just sort out the wheat from the chaff! As a new member you will probably not be able to post pics until you have made a few posts. Once you can get some pictures up the advice will be more targeted and accurate. If you are a practical type you will love this project. By the way the most important rule of boat rebuilding is to never buy equipment from a boat shop. Always find your local specialist supplier. Hydraulics, stainless steel nuts and bolts, fibreglass, timber, plumbing, electrics, etc. etc.

Thanks for the info - there is so much knowledge available on here.

In the 4 years I have contemplated this project I have amassed a library of books and technical information from the 'web but know I will need expert technical assistance at some point and have budgeted for that - I would like to have a marine engineer / surveyor 'on board' to confirm my ideas and processes prior to my doing something silly.

Definitely avoiding chandlers! Fortunately I'm moving from London to the South Coast so hope to find the specialist suppliers I need down there - there's naff all up here except expensive boatyards on the Thames.
Most of the materials I need seem freely available on the internet.

The superstructure modifications, (additional frames, ply deck and stainless tube reinforcement) engines / drives / fuel tank installation use 'off the shelf' components - the fun part will be making up the various period related lights, masts, deck equipment etc, that's what I'm looking forward to the most; i.e. a searchlight made from a pressure cooker vessel, suitably drilled and tapped for mountings with a sealed beam unit; a demountable radar mast, a mast for multiple 1960 era 'Perko' nav lights, of which a master mould will need to be created for resin cast replicas; mounting for (replica) twin 50 calibre M2 machine guns in the bow etc....

 

[Nike55]

Where are you planning to use the boat? Dropping twin petrols into a boat that has no engines at all sounds daft to me when diesel is so much safer and easier to get beside the water, would that be a project 31 hull? Although they were generally on outdrives I know of one on the broads that has a single inboard MD32 volvo on a Vee drive so the engine is in "backwards" and the shaft exits at a good angle underneath, made a great broads boat.
If only using on rivers a single outboard on a frame would be the way to go.

Won't be using it too much and not going that far. Tidal rivers mostly, a bit of shallow coastal for transits to and from rivers, not planning on crossing the Atlantic.

Twin petrols are quite common - but agree not as common as diesels, besides that's what I have at the moment - I could swap to a diesel sometime in the future should I want to.

I might even chuck in a 50 hp Kubota as a 'wing engine' for trolling, I have the space.