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19 April 2015, 16:35
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#1
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Member
Country: Ireland
Length: no boat
Join Date: Mar 2015
Posts: 39
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What size auxiliary?
As above what are ur using on your 6m RIBs?
In the market for one of these, thinking 8hp.. Would 15 be too big?
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19 April 2015, 16:50
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#2
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Member
Join Date: Jun 2010
Posts: 2,934
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often the problem is what size physically fits.
assuming you have plenty of room then a 9.9 would be pukka, or if you can manage the 15hp in terms of transom weight/fitment then, why not!
8hp upwards would be good though if you have room.
cheers
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19 April 2015, 17:15
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#3
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Member
Country: UK - England
Town: Retford
Boat name: Spy-sea-one
Make: Excel 435
Length: 4m +
Engine: Suzuki Outboard/25/4
Join Date: Oct 2011
Posts: 7,508
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Got a 4hp suzuki on mine couldn't go any bigger on width fixed on the transom not on bracket gives me 3.5knots 6m x 2.4m beam use main engine to steer I find my double 60mm A frame a pain to use the aux on the bracket so fixed to transom.
Reason for 4hp bought it for small sib best of both worlds
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19 April 2015, 17:49
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#4
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RIBnet admin team
Country: UK - England
Town: The wilds of Wiltshire
Boat name: Dominator
Make: SR5.4
Length: 7m +
Engine: Yam 85
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Posts: 13,067
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15 is pointless. You'll never plane with an auxiliary, so all you need is enough to reach the displacement hull speed.
8hp is enough for my 7.8m, so will be plenty on a 6m.
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19 April 2015, 18:35
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#5
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Member
Country: UK - Scotland
Town: Girvan & Tayvallich
Boat name: Breawatch
Make: Ribcraft
Length: 5m +
Engine: Mercury 150 F/stroke
MMSI: ex directory!!
Join Date: Sep 2008
Posts: 6,203
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Quote:
Originally Posted by Nos4r2
15 is pointless. You'll never plane with an auxiliary, so all you need is enough to reach the displacement hull speed.
8hp is enough for my 7.8m, so will be plenty on a 6m.
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Agree with Nos you'll just create froth and get nowhere fast. I have a 4hp fourstroke on mine and has proved itself. So your eight will be okay
Sent from my iPhone using RIB Net
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jambo
'Carpe Diem'
Member of the ebay Blue RIB cover club
Member of SABS ( Scottish West Division)
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20 April 2015, 07:00
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#6
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RIBnet supporter
Country: UK - England
Town: Rutland
Length: no boat
Join Date: May 2006
Posts: 2,500
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Quote:
Originally Posted by Nos4r2
15 is pointless. You'll never plane with an auxiliary, so all you need is enough to reach the displacement hull speed.
8hp is enough for my 7.8m, so will be plenty on a 6m.
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15 is great when your having to toy another 7m into deeper water
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20 April 2015, 07:08
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#7
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RIBnet admin team
Country: UK - England
Town: The wilds of Wiltshire
Boat name: Dominator
Make: SR5.4
Length: 7m +
Engine: Yam 85
MMSI: 235055163
Join Date: Jul 2005
Posts: 13,067
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Quote:
Originally Posted by bedajim
15 is great when your having to toy another 7m into deeper water ![wink](https://www.rib.net/forum/images/smilies/wink.gif)
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Fair. What did Mollers do?
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20 April 2015, 11:13
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#8
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RIBnet supporter
Country: UK - England
Town: Rutland
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Posts: 2,500
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Quote:
Originally Posted by Nos4r2
Fair. What did Mollers do? ![wink](https://www.rib.net/forum/images/smilies/wink.gif)
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He was being sensible ![roll eyes](https://www.rib.net/forum/images/smilies/rolleyes.gif) saving our big whisks in very shallow water
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20 April 2015, 14:09
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#9
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RIBnet admin team
Country: UK - England
Town: The wilds of Wiltshire
Boat name: Dominator
Make: SR5.4
Length: 7m +
Engine: Yam 85
MMSI: 235055163
Join Date: Jul 2005
Posts: 13,067
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Quote:
Originally Posted by bedajim
He was being sensible ![roll eyes](https://www.rib.net/forum/images/smilies/rolleyes.gif)
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Are you sure there wasn't a slightly sarky undertone to it?
To be fair, I think my 8hp would probably do it too-all it does is make foam on the top 1/3 of the throttle.
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20 April 2015, 14:14
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#10
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RIBnet supporter
Country: UK - England
Town: Rutland
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Quote:
Originally Posted by Nos4r2
Are you sure there wasn't a slightly sarky undertone to it? ![wink](https://www.rib.net/forum/images/smilies/wink.gif)
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You mean saving his engine, never thought of that
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20 April 2015, 14:22
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#11
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RIBnet admin team
Country: UK - England
Town: The wilds of Wiltshire
Boat name: Dominator
Make: SR5.4
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20 April 2015, 14:23
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#12
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Member
Join Date: Jun 2010
Posts: 2,934
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my 8hp yam will run flat out no probs.
i don't see how anyone can say 15hp is too much, i've seen boats with the same size aux as the main engine!
cheers
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20 April 2015, 14:45
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#13
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RIBnet admin team
Country: UK - England
Town: The wilds of Wiltshire
Boat name: Dominator
Make: SR5.4
Length: 7m +
Engine: Yam 85
MMSI: 235055163
Join Date: Jul 2005
Posts: 13,067
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Quote:
Originally Posted by Xk59D
my 8hp yam will run flat out no probs.
i don't see how anyone can say 15hp is too much, i've seen boats with the same size aux as the main engine!
cheers
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Let me put it this way. On my 7.8, the 8hp will give me 6 knots at WOT.
On my SIB, it'll give me about 15 knots.
That means I'm shoving water astern at an extra 9 knots that I don't need to be when it's at WOT being used as an auxiliary.
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20 April 2015, 14:53
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#14
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Member
Join Date: Jun 2010
Posts: 2,934
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well if you strap your 225 opti on your sib it will probably be double what your rib gets!
there is nothing wrong with a big aux if-
1. have room for it
2. transom can support it
3. can be bothered lugging about the extra weight to/from the boat.
if it froths the water then twist the throttle back a smidge..simples.
9.9-15hp would be my ideal if i had room, opens up SIB options if nothing else.
cheers
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20 April 2015, 18:24
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#15
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RIBnet admin team
Country: UK - Scotland
Boat name: imposter
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Engine: Tohatsu 30HP
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Quote:
Originally Posted by Xk59D
well if you strap your 225 opti on your sib it will probably be double what your rib gets!
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No, because he'll have it propped right for the job it normally does... You can't go any faster than the prop.
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20 April 2015, 19:03
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#16
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Member
Join Date: Jun 2010
Posts: 2,934
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Prop the 15 accordingly then
Cheers
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20 April 2015, 21:24
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#17
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RIBnet admin team
Country: UK - England
Town: The wilds of Wiltshire
Boat name: Dominator
Make: SR5.4
Length: 7m +
Engine: Yam 85
MMSI: 235055163
Join Date: Jul 2005
Posts: 13,067
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Quote:
Originally Posted by Xk59D
Prop the 15 accordingly then
Cheers
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I don't think you can actually get a prop for a 15hp thats pitched that low.
You're welcome to prove me wrong though-I haven't checked on prop sizes for a 10-15hp for a couple of years and it wasn't a massive concern when I did.
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20 April 2015, 21:39
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#18
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Member
Join Date: Jun 2010
Posts: 2,934
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wouldn't bother with it.
if i had a 15 then i'd just live with it at 3/4 throttle.
however, there are prop options available if you wish to do it.
Mercury 15hp Propellers, 2 Stroke - prop charts)
anyways, no need to keep going round in circles, there is no need for a 15hp on a 6m boat, a 5hp would work!
the point is the 15 would work if the OP wanted it to.
personally, i'd get upto a 9.9.
cheers
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27 April 2015, 16:55
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#19
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Member
Country: UK - England
Town: Hertfordshire
Length: 7m +
Join Date: Aug 2014
Posts: 54
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4hp would be fine but if it is also for a sib/smaller rib get a 9.9 2 stroke tohatsu.
The 18hp tohatsu weighs the same and is the same size but is only needed if used on a sib as well.
Also if you get a 4hp get a four stroke. My neighbour has a 4hp two stroke for his 20ft Sea Ray and it is so so noisy, sounds like it's always under a lot of stress.
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27 April 2015, 17:08
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#20
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RIBnet admin team
Country: UK - England
Town: The wilds of Wiltshire
Boat name: Dominator
Make: SR5.4
Length: 7m +
Engine: Yam 85
MMSI: 235055163
Join Date: Jul 2005
Posts: 13,067
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Quote:
Originally Posted by Whizzbang
4hp would be fine but if it is also for a sib/smaller rib get a 9.9 2 stroke tohatsu.
The 18hp tohatsu weighs the same and is the same size but is only needed if used on a sib as well.
Also if you get a 4hp get a four stroke. My neighbour has a 4hp two stroke for his 20ft Sea Ray and it is so so noisy, sounds like it's always under a lot of stress.
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That's because it IS always under a lot of stress-as will be a fourstroke. You absolutely won't get away with a 4hp aux on a 6m rib.
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