smallest RIB with an inboard

Witwill · 10 September 2002, 20:59

I would be interested to know what the smallest RIB is that has sucessfully installed an inboard engine. As a rule of thumb would you normally think of increasing the power output by say 10% (or more?) when going to an inboard (due to the extra weight)?

I have a 5.3 Humber Attaque. The plate on the hull says the max engine size is 75HP. I have run it for the last 5 years with a 90HP outboard and it's been great!

I am considering (now the 90HP has gone to the great outboard land in the sky) fitting an inboard on an outdrive. Do you think that the RIB is too small? If not should I be fitting a 120HP inboard or maybe bigger !!?

I would love to know what folks think!

Thanks all.

Alan · 10 September 2002, 21:25

Yes I think its too small and the engine would be too heavy and take up too much room. Smallest RIB with a diesel I've seen is 6m.

Alan

Garygee · 10 September 2002, 21:31

Hi,

Take it your talking about the 120Hp 1.7 TD from Mercruise.

Not a master on diesels but the smallest I have seen this in is a 6.5M RIB.

Also the room taken up inside the boat will be about 3 feet !, plus the extra weight, over twice as heavy as the same outboard.

Small RIBS suffer from stern heavy problem with twin small outboards, say twin 50Hp at about 100Kg each (200Kg), never mind a 300Kg diesel.

Also if the max is 75Hp going to 120Hp may be too much.

See what other people think but i would think you would need a bigger boat for that engine.

Either way this could be a interesting thread to watch

Regards Gary

Witwill · 10 September 2002, 22:00

Thanks for the replies so far. In fact I am planning on an inboard PETROL engine and not a diesel. I am thinking about keeping it as small as I can and as light as possible.

Wakie idea too far ?

Keith Hart · 11 September 2002, 08:46

Hmmmmmm, haven't I seen an outboard diesel somewhere?

Keith (memory is fading a bit) Hart

GraemeCooper · 11 September 2002, 10:44

There was an Outboard Diesel that was popular on the inland waterways some years ago, but the max size was 35HP.

Not sure if technology has moved on - guess it depends on the need for such a beast.

Jelly · 11 September 2002, 11:44

Sorry to digress from string, but Yanmar makea 27 & 36 diesel outboard as we use them on the ribs / inflatables / small work boats offshore. Reason is that we aren't allowed petrol OB's in the oilfields the company works in and yes they are very heavy for size and very slow!
Jelly

Pete7 · 11 September 2002, 18:49

The Sea Cadets at Lymington had a Humber attack with an inboard diesel (mid mounted) and a jet drive some years back, although it was up for sale at the time. Also there are those over grown jet ski things with have proper seats driven by outboard engines mounted internally on a jet. However on a small rib the balance is going to be the problem. The Ford 2.5L 4 cyl D (70 - 140 Hp) weighs in at 248 kgs and thats without the jet or stern drive at another 100 kgs. I think for simplicity and cost on a small rib then an outboard is going to be hard to beat.

http://www.lancingmarine.com/

Now if they produce a rib version of the 5.4m with a small jet we could be talking, perhaps a motorcycle engine ?

http://www.working-boats.co.uk/

John Kennett · 12 September 2002, 09:40

The smallest inboard RIB has got to be the Avon Seasport Jet 320 at (you guessed!) 3.2 metres long.

It's powered by an 83hp 2 cylinder, 2 stroke Yamaha inboard!

Mercruiser also produce a very compact jet drive unit designed for PWs and small boats, but as far as I know it's only available to manufacturers of boats approved by Mercruiser.

John