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Old 29 August 2014, 18:13   #1
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Country: UK - Scotland
Town: north ayrshire
Boat name: charlie girl
Make: reiver 3.8/regal3760
Length: 10m +
Engine: 40hp 2st 2x6lp 315
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Posts: 1,502
minimum size hull for 250hp diesel

Hi I'm fancying a bigger rib to play with & have a 250hp merc D-Tronic& bravo drive doing nothing I want to match a hull to the engine & just wondering what size hull to look for
I'd like it to be reasonably quick so the lighter & smaller the better but obviously it has to carry the weight of the engine
also apart from the necessary alterations to the hull is there any down side in converting an outboard hull to inboard (I'm thinking legally) and how outboard hp rating would translate to inboard
I'd expect a given hull would cope with more hp inboard than outboard or do I have that wrong?
Cheers
Ken
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Old 30 August 2014, 03:30   #2
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Country: UK - England
Town: Margate / Ramsgate
Boat name: Ballistic
Make: Ballistic
Length: 7m +
Engine: Yam HPDI 250
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Transom angle and thickness critical for a drive installation, apart from that I've often thought cutting open a deck modifying stringers amd bulkheads to make engine mounts and making an engine box would be all that's involved ??? But never done it.

It's the weight of the diesel lump and drive that's going to affect hull choice - and a 250 diesel + bravo will be a lot heavier than a 250 old skool 2 smoke / even an opti or 250 4-stroke won't it so I'd say you're looking 8m +

Something with a good beam to carry the weight and acomidate an engine box too.

If you'd the budget I would say a new hull from someone accommodating yet affordable like osprey or humber would be the way to go.

It would be an interesting build thread.
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Old 30 August 2014, 04:31   #3
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Country: UK - England
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Boat name: Fugly & Rokraider 1
Make: Pac 22 & Porter 6.5
Length: 6m +
Engine: Ford 250 & jet,DT140
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You will need to have strong main chassis rails to mount the engine on. Probably be better in the long run to buy an existing inboard RIB with a blown engine?
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Old 30 August 2014, 04:42   #4
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Boat name: stormchaser
Make: custom rib
Length: 8m +
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7.8 metre upwards for an engine that size, the engine drive etc will weigh in at about 600 kilos, where the drive sits lower than a outboard you will only have to make the top up, the whole boat will behave differently as the CG will be lower and further forward than an outboard boat, I'm doing a blank boat now, transom was too thick and it has no beds in it yet, I've cut in the shield and lined the engine up to workout the best way to put in the bedsClick image for larger version

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ID:	98383, had to cut the forward bulkhead out as well
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Old 30 August 2014, 05:00   #5
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Quote:
Originally Posted by Rokraider View Post
You will need to have strong main chassis rails to mount the engine on. Probably be better in the long run to buy an existing inboard RIB with a blown engine?

Not strictly true, half the engine hangs on the transom, the fwd engine mounts are resting on what will be new beds and these are usually glassed onto the stringers and down onto the hull, as this will all be new you can make it as strong as you like, but you're a little right in as much as some boats will be light on layup and need more work
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Old 30 August 2014, 10:38   #6
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Country: UK - Scotland
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Boat name: charlie girl
Make: reiver 3.8/regal3760
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Engine: 40hp 2st 2x6lp 315
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Been offered a 6.5m tornado which formally had 275 outboards which is a tidy ish boat & a 21' BWM which had a 4lh & Jet drive
I've no problem with the structural mods to the outboard boat & pretty sure transom angle for outboard is very similar spec to sterndrive but not sure how it will carry the weight? Any ideas?
The BWM has tired (but not knackered) tubes but should be ok with the weight as the 4lh is a lardy lump anyway would need to check the transom angle as I think some jets use straight transoms
Personal preference would be the tornado as it has better tubes
I'd rather not go too big as the merc D-Tronic isn't the strongest engine to lug around a heavy boat I wouldn't expect it to be any quicker with the 250 inboard than it was with the 150 outboards taking in to account the weight penalty
Any opinions?
Cheers so far!
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