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Old 14 April 2015, 09:42   #1
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Few questions.Rib project

Hi ,
started a project and would like some answers and advice:
1) is this ex rnli boat?how to tell?is it a good rib?
2) what material is the tubes?
3) would this engine be powerful enough for divers boat? 5-6 divers plus gear?
4)engine shaft is 20 inch .rib transom is about 27 so i have to cut to fit it.is it ok to do that?or i better look for 25 inch engine shaft?
i know,i know too many for the first post,but season is nearly there so i have to be quick.
thanks in advance.
regards
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Old 14 April 2015, 10:46   #2
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more experience will be along shortly,
I would say, not RNLI (maybe used by in some capacity but not as a rescue boat).
I think Cobra are Hypalon I'm sure some one will poke me if i'm wrong
Cant see clearly the HP I would say min 150 hp needed.
Seven inch is a lot to cut out i would say look for an engine closer to the correct length.
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Old 14 April 2015, 11:58   #3
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Quote:
Originally Posted by abyss View Post
Hi ,
started a project and would like some answers and advice:
1) is this ex rnli boat?how to tell?is it a good rib?
2) what material is the tubes?
3) would this engine be powerful enough for divers boat? 5-6 divers plus gear?
4)engine shaft is 20 inch .rib transom is about 27 so i have to cut to fit it.is it ok to do that?or i better look for 25 inch engine shaft?
i know,i know too many for the first post,but season is nearly there so i have to be quick.
thanks in advance.
regards
Hi! Welcome to the madhouse!

I'm at work at the mo, so can't enlarge the pics too much -hence 2 Qs - How big is the boat (I guess 6.5-ish m?) and how many Gee Gees is that engne? - I guess somewhrere round the 130 mark from the shape?

Re./ the transom height / engine leg length- I reckon that hull was set up for twins based on the fact the "lip" is missing in the locations I would expect you would want to park a pair of engines. Now, this is where the measurements get fun:

Measure the depth of the transom at the midpoint of those two cutouts - I'll bet the depth is 25 inches.


I'll need to hand you over to the tank carrying brigade (I don't dive!) but beofre you start sawing the transom around - and assuming that is a 6.5m or bigger hull & 130 odd HP engine, do you actually want to be looking for a twin for it? (Although they are not a young design so that may be a bit more difficult than it looks unless you don't mind resuscitating engines!)


And before the "twin vs single debate starts again - if the transom is set up for a pair, why @rse around with it & risk a leak / rotten transom? Especially as those Clamshell type engines were remarkably light for their HP.
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Old 14 April 2015, 11:58   #4
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It's 135 hp mariner.
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Old 14 April 2015, 12:11   #5
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It's a 7m long if measured with the tubes.135 hp 2 stroke.
Don't have to fly with it.just runaround with my fellow divers. Don't want to spend xxx amounts of $ too.so if it's safe to put something out of what I have and it will work I will do it.
Have no problems to fabricate most of the hardware for the project .
It's my first boating experience ...
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Old 14 April 2015, 12:44   #6
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Welcome to Ribnet Nice looking hull.


This may sound a little negative I'm afraid.

What you've got there is a hull and motor that really shouldn't go together. The hull is set up for twins, and realistically cutting the transom down may reveal/cause things you don't want happen.
135hp isn't really enough HP for that hull, and that old motor is going to use a LOT of fuel-more so as you'll be caning it to get it to go with 5-6 divers+gear and cox. I'd expect 50 litres per hour or more.

Essentially, either get a motor/motors that'll fit the hull you have (which would be desirable), with at least 175hp and newer tech, or get a hull that'll go with that motor (less desirable but cheaper inital outlay).
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Old 14 April 2015, 13:09   #7
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Just to add to what's been said, there's no way would I cut a transom down on a dive boat. When you get loaded up, freeboard is everything. You get some lardy @rsed diver kitting up at the stern & it soon starts getting very wet.


.....sh1t happens.......
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Old 14 April 2015, 13:56   #8
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135hp isn't really enough HP for that hull, and that old motor is going to use a LOT of fuel-more so as you'll be caning it to get it to go with 5-6 divers+gear and cox.
Same as the Mercury on my hardboat - 17' Dory Sportsman. They are basically a detuned 150hp. V6 2 litre with 'oil injection' - although it's really just drip-fed into the fuel line before the carbs - which has a certain reputation. Disabling the oil pump & using a 50:1 premix is recommended on some sites & appears to be a common mod. Mine's standard, but I did have the oil feed pipe split, fortunately I was drifting & fishing at the time & had the 'Where's that oil slick at the back of the boat coming from?' moment which is preferable to the 'Oh dear it's seized' one
Not exactly slow, but they ARE thirsty! I do toy with changing it & if I lived nearer the sea & used it more I probably would.
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Old 14 April 2015, 14:40   #9
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Not exactly slow, but they ARE thirsty!.
+1 My mate had one on a 585 RC & it was a thirsty, stinking beast
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Old 14 April 2015, 15:10   #10
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+1 My mate had one on a 585 RC & it was a thirsty, stinking beast
Aren't ALL Yorkshiremen!?
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