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Old 24 February 2010, 14:19   #1
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Auxiliary size?

Hi guys,
I am looking at getting a small auxiliary for my 4.5m SIB and was wondering what you guys think should be the minimum hp I 'll need?
Cheers,
Geoff
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Old 24 February 2010, 14:47   #2
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i have always been advised. if you work on 1horse power per 1m boat length that should be ok. as your rib is 4.5m
you will require a 4hp engine unless you carry plenty of weight aboard then i would be looking towards a 5hp..

but 4hp should be sufice
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Old 24 February 2010, 15:00   #3
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i have always been advised. if you work on 1horse power per 1m boat length that should be ok. as your rib is 4.5m
you will require a 4hp engine unless you carry plenty of weight aboard then i would be looking towards a 5hp..

but 4hp should be sufice
that is the 'rule of thumb' but bear in mind that fitting a 4/5 HP engine beside your main engine may be impossible. In which case it will be 'whatever fits' rather the best size. 4m boats seem to move OK, but not fast with 2HP unless you are in nasty conditions or tides which is probably less likely with a small boat.
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Old 24 February 2010, 15:21   #4
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Thanks guys,
I had heard the foot per meter rule but had hoped I would get away with less as the boat is light.
Is the difference between a 2hp and a twin cylider 4hp a lot?
It is going on a auxiliary bracket mounted on the back, but only when needed.
Cheers,
Geoff
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Old 24 February 2010, 15:42   #5
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Hi there Geoff ,You are gonna have quite bit of weight on the transom with both outboards,if you are gonna have both ,they will both have to combine to the given overall weight that your sib transom can take, i would of thought ,have you the infomation plate on the transom with the specifications of the sib?my 3.3 is a cracking 2 stroke light outboard,,would you have to carry even more fuel ,more weight again? just a thought
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Old 24 February 2010, 15:46   #6
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Hi there Geoff ,You are gonna have quite bit of weight on the transom with both outboards,if you are gonna have both ,they will both have to combine to the given overall weight that your sib transom can take, i would of thought ,have you the infomation plate on the transom with the specifications of the sib?
It takes 55hp, and my main engine is a 25 two stroke, so I think it will be fine.
I know a lot of people think it is not a good idea for me to have an aux, but I am intending on going further afield, and I REALLY don't want to have to rely on other people coming to my aid if I breakdown.
Cheers,
Geoff
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Old 24 February 2010, 17:06   #7
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I reckon something like Thorny's 3.3 would do you nicely-as you say your boat is quite light.
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Old 25 February 2010, 08:14   #8
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I had heard the foot per meter rule ...
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Old 25 February 2010, 10:24   #9
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if theres not a lot of room on the transom you could always keep it up front in the bow, coverd up with a tarp or a large holdallall , keep it nice and dry should you need it , ,it will keep the balance right a bit of weight in the bow too if your on your own ,,,i used a 4 hp johnson as aux on a 16 foot humber s.i.b. that i used to have , and i got around 4knots out of it ,put a mariner 4 hp on and got 6 knots .
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Old 25 February 2010, 12:21   #10
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Originally Posted by Geoff_Jubb View Post
Hi guys,
I am looking at getting a small auxiliary for my 4.5m SIB and was wondering what you guys think should be the minimum hp I 'll need?
Cheers,
Geoff
Geoff my 3.3 mariner is very light and a real work horse ,good for were i use her ,but with a good tide run really have to push her ,but she gets me along,i will be testing her on the new addition sib that i will be getting see how she performs on a longer sib,i will be after getting a new engine ,but a bigger one,but for lightness yes 3.3 mariner dam good
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