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Old 19 September 2002, 10:14   #1
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Country: UK - England
Town: Bromley, Kent
Make: GS209
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Spare engine mounting help needed

I am having a 9.8hp 2 stroke put on a 6.6mtr RIB as a spare. I understand that I will need to get a long shaft model, and that it should have a 'High thrust prop' (you would never believe a week ago I knew nothing about boats). I have also heard to my dismay that my plan to also use the 9.8hp on a SIB is out of the question because of the long shaft, unless I raised the back bit of the SIB or whatever with a 'raiser' (if that is the term) which would then give the correct speed but knacker the boat quicker.

My concern is that apparently these RIB's bash about a bit, I was told that a good idea is to put the engine on back to front and then strap the bottom bit to the transom inside the boat, this should stop it bashing about.

I was also told that a 5hp could push 2 tons and that as the 9.8hp would not get a 6.6mtr on the plane, and there is only a maximum speed that the hull will go off the plane, that it would be a waste.

Boy this is a nightmare, but I am determined to learn from you lot, my brain is hurting and I have not even started my RYA 2 course yet.

Sorry to clog up the site, but any wise suggestions on this??

Pete (nearly done)
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Old 19 September 2002, 10:48   #2
DJL
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The problem with having the engine mounted back to front is that when you need it you have to take it off the transom and turn it round; lifting a 9.8HP engine in rough seas won't be that easy. I jam a piece of wood on the end of a piece of bungy cord into the tilt mechanism to stop it bouncing.

As to the size of the engine. While at the boatshow on saturday looking at a 27ft Targa (large boat - Picture ) they suggested that a 6HP be used as an aux engine and I can't imagine that it would go anywhere with that. I have a 4HP on my 4.7m RIB and get around 6kts at WOT. If you can I would try any engine before buying, I got alot better performance from a 4-stroke 4HP than a 2-stroke 4HP from the same manufacturer! plus having a 4-stroke allows me to run it off my main fuel tank.

You need to check the height of your trasom to see if you need long or short shaft. I use a short shaft on my RIB and it fits perfectly with the anti cavitation plate a few mm below the hull.

Daniel
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Old 19 September 2002, 11:03   #3
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Country: UK - England
Town: Dartmouth
Boat name: Puffling
Make: Avon Rover 3.4m
Length: 5m +
Engine: Mercury 15hp
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I have tried with a 2hp Honda on a 4 metre...there is not alot of room on the back end...I got it on only to find after 2 hours it was just about to fall off...I don't have a dedicated bracket...just strapped it on...Possibilty is to get an adustable height outboard bracket that usually has three or so settings...Boling thisa to the transom allows engine height to be change...
2hp pushed RIB along albeit at only about 4 knots...
Used to have a Shetland 535 with a 70's 4 hp 2 bladed 2 stroke that did 6.5 knots....
I would say on a 6 metre boat 5-6 hp is a good size...two stroke generally has more power...(controversy to follow!!)
I was at gym when u phoned last night did not get message till 11pm...
Tohatsu 90hp is the slimline one so hopefully there would be enough room on transom for Aux...
Alternately make an attachment on the console jockey back rest...as in some race ribs the Aux engine is inboard... then mounts on back end if needed...also puts the weight in the centre of the boat..
As for sunday...Not sure what am doing yet...so if u have someone else that is best...If not ring on saturday will have mobile on all day and shall see if am free Alex
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Old 19 September 2002, 11:08   #4
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Country: UK - England
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Does it have to be a Tohatsu...6m...
There is a nice Ribtec 6 metre on the boats for sale page...twin 60hp...Better relaibility get u home.....
Money saved allows for more modifications to get best setup...
Ribtec are a good breed...
Alex
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Old 19 September 2002, 11:14   #5
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My 2p's worth.
Don't bother with an aux. more pain etc than it's worth (banging about, two fuels, takes up room, more things to go wrong/buy/service etc).
Why do you need it? In case engine no1 fails?
Get yourself an anchor, a sea anchor and a VHF.
If main fails,shout for help. If in immediate danger, anchor and shout louder.
PS Longshaft works fine on a SIB, just take care when opening the throttle thats all.
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Old 19 September 2002, 11:25   #6
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One of the guys where I work always reckoned on something like 1hp per metre with aux engines...... but, my parents Hardy (6.4m) only had a 4hp 2 stroke on the back, which propelled it along just fine in most weathers.

I'm looking at getting a 6m Humber in the next month or so, and was hoping to stick a 4hp 4 stroke on the back, but I'm not sure as yet whether I'll have to put a proper aux bracket on the back, or if the engine will mount directly onto the transom (which I'd prefer). I'm actually hoping Humber will know the best solution for this.....

-Alex

(first post - yay!!)
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Old 19 September 2002, 11:31   #7
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I had a 6hp, but it was a pain in the ar** whenever there was a slight ripple - tried to fall off, tried to jump out, bounced on my foot...then i changed to a 3.3hp, BUT to be honest i rarely take it with me (silly really) and go with Brians option...

I have two VHF's, two sea anchors, two anchors and a VERY loud voice - oh, and i buy the lifeboat crew beer when i see them in the pub!

Oh, one final comment - ribtec w/ twin 60's - nice setup and worth considering...
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Old 19 September 2002, 12:29   #8
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Flanker

I use this method in order to hold the engine really unmovable. This way the engine is mounted on another bracket with it's leg strapped on it's working place. Of course I have to move it from the one bracket to the other IF something goes wrong with the Merc. (Never so far).
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Old 19 September 2002, 12:51   #9
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Great idea, but see my last post re on the rocks

Pete
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Old 19 September 2002, 12:57   #10
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Hi,

On my RIB, I have found that to mount the wing motor (a Malta - quite adequate) in the bow on a specially made bracket helped (see picture). I really wouldn't feel comfortable going outside the Solent without an auxiliary.

Re your other thread - I also find a Hydrofoil on the main engine gets the boat up on the plane much quicker - an advantage to be able to plane at 10 knots in Portmouth harbour

Rgds

Nigel
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