What size auxiliary?

Johnny1 · 19 April 2015, 17:35

As above what are ur using on your 6m RIBs?

In the market for one of these, thinking 8hp.. Would 15 be too big?

Xk59D · 19 April 2015, 17:50

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

jeffstevens763@g · 19 April 2015, 18:15

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

Nos4r2 · 19 April 2015, 18:49

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.

jambo · 19 April 2015, 19:35

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.

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

bedajim · 20 April 2015, 08:00

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.

15 is great when your having to toy another 7m into deeper water

Nos4r2 · 20 April 2015, 08:08

Quote:

Originally Posted by bedajim

15 is great when your having to toy another 7m into deeper water

Fair. What did Mollers do?

bedajim · 20 April 2015, 12:13

Quote:

Originally Posted by Nos4r2

Fair. What did Mollers do?

He was being sensible

saving our big whisks in very shallow water

Nos4r2 · 20 April 2015, 15:09

Quote:

Originally Posted by bedajim

He was being sensible

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.

bedajim · 20 April 2015, 15:14

Quote:

Originally Posted by Nos4r2

Are you sure there wasn't a slightly sarky undertone to it?

You mean saving his engine, never thought of that

Nos4r2 · 20 April 2015, 15:22

Xk59D · 20 April 2015, 15:23

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

Nos4r2 · 20 April 2015, 15:45

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

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.

Xk59D · 20 April 2015, 15:53

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

Poly · 20 April 2015, 19:24

Quote:

Originally Posted by Xk59D

well if you strap your 225 opti on your sib it will probably be double what your rib gets!

No, because he'll have it propped right for the job it normally does... You can't go any faster than the prop.

Xk59D · 20 April 2015, 20:03

Prop the 15 accordingly then

Cheers

Nos4r2 · 20 April 2015, 22:24

Quote:

Originally Posted by Xk59D

Prop the 15 accordingly then

Cheers

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.

Xk59D · 20 April 2015, 22:39

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

Whizzbang · 27 April 2015, 17:55

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.

Nos4r2 · 27 April 2015, 18:08

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.

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.