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Old 04 May 2001, 01:31   #1
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Aux Engine for RIB

I have a Lencraft 5.5 and am looking to purchase an auxilliary engine. I have been told that the Tohatsu 3.5 longshaft is a good little unit and is more powerful than the size suggests. Its on offer new at 395 GBP.
Has anyone any particualr experience with this engine and is it available cheaper anywhere in UK.
Thanks
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Old 04 May 2001, 18:19   #2
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Certainly you will need a long shaft .

Irish Sailing Association and RYA guidelines for Aux engines for RIBs are that you should have at least one HP per metre lenght of RIB.

Another consideration is the fuel supply for the Aux engine which will probably require premix while your main engine may be autolube .

Best wishes ,

Stuart www.powerboat.org

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Old 05 May 2001, 02:57   #3
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Thank you very much for this. From what i hear of the Tohatsu, although a 3.5 it has the output nearer to a 5, so I should be ok.
Fuel-yes, we will have to carry a spare gallon, but always do so, oil will be stored in bottle for a mix.
Cheers
Dave
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Old 05 May 2001, 05:10   #4
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Dave
Quote:
although a 3.5 it has the output nearer to a 5
I have heard good reports of this motor, but I would be surprised if this really is true.

If it is, then how many hp would the "5hp" engine produce, given that its cylinder capacity is 35% greater than the "3.5"? The 3.5hp engine is actually the same capacity as the 2.5!

According to the Tohatsu web site www.tohatsu.com/outboards/ the 2.5 and 3.5hp motors are both 74.6cc and the 5hp is 102cc.

I would be surprised if the 3.5 would get you anywhere against a tide. It might make a reasonable anchor though . . .

John
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Old 05 May 2001, 12:44   #5
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John, I am most grateful for the info. I have only the word of the vendor on this, and his ca,parisons are against "other similar sized engines". I am not under any particular pressure to but the To'su and if you can suggets another make engine which is better suited to needs and is about 400GBP, I would love to hear from you.
Dave
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Old 06 May 2001, 04:29   #6
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Dave

I would say that you need at least a 5hp engine. If your dealer reckons that a 3.5 will do the job, then see if you can get a trial with one and see how well it copes. If it does turn out to be up to the job then let us know and we'll eat humble pie. Don't forget that when you actually need to use it you are bound to be in poor conditions going against the tide (sod's law!), so make sure your trial is realistic.

There's no point buying an angine that's too small just because it's cheap. How much is a 5 or 6 hp Tohatsu? If you can't afford a new engine that is big enough, then it would better to either wait until you can or buy second hand. A reserve engine that is too small to get you home is just so much ballast.

Let us know how you get on!

John
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Old 07 May 2001, 15:58   #7
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We have a Yamaha 5hp 2 stroke as the aux to our 6.5m BWM RIB. Flat out she will make around 4-4.5kts. When our main engine failed Good Friday we only just could make it into Portsmouth Harbour against the Ebb. And I mean only just!

In my humble opinion you need an aux that will push you at 4kts at least. And then you need the understanding that if neccesary you are going to have go with the tide rather than neccessarily go where you want to! (In my example Portsmouth was the only place we could go as we were only a mile off when the main failed.) The other key thing is to keep the aux well serviced and in tip top condition. It needs to start first pull when you need it otherwise all you are doing is hauling around extra weight!

Just my 10 penn'orth!

alan
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Old 08 May 2001, 01:17   #8
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Alan, thanks. Looks as though the RIB will have a 5 slung over the back.
Good to share views on the matter.
Dave
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