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Discussion Starter #1
Hi all

I'm after a bit of advice and was hoping there might be a few people out there who might be able able to offer some advice.

Our club rib is a 5.8m wide bodied tornado with a 115hp 4 stroke outboard on the back, I'm thinking of fitting an auxillary engine (via an auxillary outboard bracket) to the transom, so that in the event of an primary engine failure we've got enough back up to motor around and pick up any divers in the water. I'm not expecting the aux' engine to be powerful enough to get the boat onto its plane.

I've been looking into sizing a suitable engine and at the moment have suggestions from 4hp to 15hp, so my question is does anyone out there have a similar set up and if so how big is the aux' engine and how does it perform.

all comments appreciated

GMC
 

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Jesus don't want me for a sunbeam
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I had a 6hp on my 4m RIB. It pushed it, nowhere fast but it did at least give some power to steer with. I was advised one hp per metre of length as a minimum, although my 3hp Seagull seemed to push it reasonably well too (if a bit noisily and with an oil slick behind).

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murofevideht
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You might be surprised how little wind and wave action would make a 4hp useless on that set up. Your problem will be size. I'm guessing that you'll struggle to get anything bigger than an 8hp on the transom so it won't interfere with the main engine.

I would recommend a second 115hp :D
 

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We have a 7.25 Mtr rib with a single 150hp main and a 6.5 hp backup as said space on the transom is the issue but it moves our boat around enough to pick up divers but thats about it it would be a long journey back with it.
 

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Discussion Starter #5
thanks for the replies, space is definately the issue, but looking at some of the mounting brackets that are on the market these may give us a few more size possibilities. My current thinking is to mount a bracket and then see if we can try out some engine sizes (a few mates have 4's & 6's) to see how they perform.
 

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Squidgey Member
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I had a 5HP seagull as a back up engine on a 5M hard boat (Orkney) The boat was heavy and had three persons onboard it got us 14 Miles back from the Edystone eventually.
 

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I use an 8m Alu/HDPE RIB style jet boat, It's not too light. An 8hp with a high thrust prop gives us 5-6 knots, and reasonable turning. It will get us home but I wouldn't like to try a long trip in bad weather.....might take some time to get back.
 

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Jesus don't want me for a sunbeam
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I had a 5HP seagull as a back up engine on a 5M hard boat (Orkney) The boat was heavy and had three persons onboard it got us 14 Miles back from the Edystone eventually.
I bought my Seagull from a guy that hadn't run it in 15 years. The fuel tank was fuel of varnish and it started on the 3rd pull.
 

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Not many Mackerel but all a good size
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I've fitted an auxiliary on something as small as a 4m squishy. On the plane it takes an auwful bashing. Used it in anger one time to return to Beesands from Prawle point. You could only lower one engine at a time, being clamped on you could shuffle the main to one side and deploy the Aux.

I currently use a 5.8m Humber Destroyer with a 115hp on it and there def wouldn't be room.

Another option is to mount the aux on the bottle rack/ front of console until required.

Question.

If you are limping home on the auxiliary will the fuel last out?

In an emergency situation any safe shore fall is a good one - you may need to go with the tide rather than against it. I hear all this "make a plan, follow the plan" cant but often a plan B is required when plan A fails.
 
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