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Old 12 March 2006, 19:29   #1
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Aux engine HP for 5.8 RIB

The Humber Destroyer 5.8m I am looking at buying doesn't have an auxiliary engine included, so I need to figure out what that will cost on top of the price of the boat because that will affect what I can afford to offer!

Is a 4hp enough for this size RIB in often windy conditions like we have here? (seems to be a common size of aux engine) - the current owner reckons it isn't and a 6hp would be more like it - but he has a 4hp (admittedly not his!) strapped to the boat and I know a couple of others using this size of engine.

any good suppliers recommended for second hand/recon stuff please? doesn't seem to be much point in buying a new one that will (hopefully) hardly ever be used!

thanks

Stephen
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Old 13 March 2006, 08:40   #2
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Quote:
Originally Posted by BogMonster
The Humber Destroyer 5.8m I am looking at buying doesn't have an auxiliary engine included, so I need to figure out what that will cost on top of the price of the boat because that will affect what I can afford to offer!

Is a 4hp enough for this size RIB in often windy conditions like we have here? (seems to be a common size of aux engine) - the current owner reckons it isn't and a 6hp would be more like it - but he has a 4hp (admittedly not his!) strapped to the boat and I know a couple of others using this size of engine.

any good suppliers recommended for second hand/recon stuff please? doesn't seem to be much point in buying a new one that will (hopefully) hardly ever be used!

thanks


Stephen
Hi Stephen

Get the biggest you and your aux transom bracket can handle. Many makes of motor use the same block for different sizes ie the 10 & 15 may be the same 2 pot block, just carbed, and bored differently, and will weigh about the same, so take the fifteen. I used a 10 on my 5.8 and it worked fine with the main motor trimmed up, progress was ok. At that time the 8 and 10 were the same block, and I could lift it ok. Bear in mind your room will be tight and space is also an issue. Mine was bolted behind the main centre jockey, not flat on the deck incase you take in water in a stuff. We used to rig it through the A frame when lowering at sea, and did tests regularly to hone our methods.

To my mind a 4 is 'pissing' into the wind. It also depends how far off shore you go etc. Our aux alsways has is own feul supply too I should say. We always carried neat petrol in the aux tank, and mixed 2 stroke at the last minute which gave us a handy reserve for the main engine should we have needed it. Hope that helps

Oh and PS, Buy a new one, since your life may one day depend on it, find the money somehow.

cheers
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Old 13 March 2006, 16:12   #3
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Thanks - I think space is the problem, a bit tight on the back and I don't think you'd get any decent sized engine in there unless you tipped the 115 into the water!



Not gonna go too far off shore here - there's not a lot of help around and the South Atlantic is pretty bumpy a lot of the time! The current owner reckons a 6hp would be about right, just curious to see what you guys think.

Good point on getting a new one more expense though
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Old 13 March 2006, 16:34   #4
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Stephen,,
Like to second the point re the aux motor,being a good un, for when you need it the most,
For very local, bay stuff, only run the little 4hp,from the yacht tender,have tested it,and will get you back in ok, but not too quick,and is a struggle with the breeze is up,
If going anywhere, have a 10hp which is used instead,not a great deal quicker, but will push against the tide/wind better

Tim
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Old 13 March 2006, 17:41   #5
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Saw something when I was searching (prob on here I think) that a good rule of thumb is 1 hp per metre of boat.

Dad has an old Seagull out on the farm but I don't think that will be man (or seagull) enough for the job!!
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Old 13 March 2006, 17:52   #6
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Quote:
Originally Posted by BogMonster
Thanks - I think space is the problem, a bit tight on the back and I don't think you'd get any decent sized engine in there unless you tipped the 115 into the water!


Yes you can.
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Old 20 March 2006, 09:17   #7
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Tohatsu do a two stroke 9.8hp (not the 9.9) which is very very compact. I think this would be idea for you

Regards

Mark
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Old 03 September 2006, 12:03   #8
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Just to finish this thread off....

I now have a Johnson 6hp four stroke aux (though badged Johnson it is actually made by Suzuki and is identical to the DF6 except it is white not black)

It gives about 5.5kt on a short burst (though not yet run in!) starts first pull most times and runs like a sewing machine. Very happy with the choice
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