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Old 24 October 2009, 15:23   #1
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Avon Rover 340 - 25hp 2-stroke or 20hp 4-stroke?

Evening all. New member here seeking some advice. Have just bought my first RIB (in fact, my first boat), a 2002 Avon Rover 340. It is currently a bare boat (ie no console or seating) and is fitted with an older Mariner Marathon 15hp. My intention is to fit a side console and bench seat, and to replace the Mariner with a larger, remote outboard.

The transom is rated to a max 25hp and max engine weight of 62kg. This effectively gives me the choice of a 25hp 2-stroke, or a 20hp 4-stroke. I'm not too bothered about out and out speed, but don't want to buy a 4-stroke and then find it's not powerful enough to get the boat up on the plane with two adults aboard.

Can anyone advise as to whether the 20hp 4/s would suffice, or would I need to go with a 25hp 2/s ?

Would appreciate your opinions, particularly from anyone with similarly sized and equipped RIBs.
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Old 24 October 2009, 16:42   #2
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Incidentally, I don't have the budget for a brand new engine so will be looking for a good 3 to 6 year old motor. Other than Ebay and Boatsandoutboards.com, can anyone suggest any other sites listing/advertising a good selection of (UK located) used outboards?

Cheers!
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Old 25 October 2009, 08:05   #3
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3.9 m boat with console (presumably heavier than yours) with 20HP 2str Yam happily planed in calm weather with 4 adults and 2 kids on board, 30L fuel, gear etc. So don't think you should have two much trouble whichever engine you opt for.
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Old 25 October 2009, 14:15   #4
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Incidentally, I don't have the budget for a brand new engine so will be looking for a good 3 to 6 year old motor.
If easy to find, go for a Mariner or Tohatsu 2 strokes 25 HP and retune it to 30 HP for peanuts, is same size & weight as a Tohatsu 30 HP, 52 kilos with extra 5 HP just in case.

Happy Boating
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Old 25 October 2009, 15:40   #5
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Thanks guys. Must admit, I'm more inclined toward the 4-stroke 20hp option than the 25hp 2-stroke, so good to hear your experience with a 20hp on a loaded 3.9 RIB, Polwart.

Howver, I guess it's a case now of seeing what I can find within my budget.

I'd still appreciate any recommendations on good sources for used motors. Cheers!
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Old 25 October 2009, 15:51   #6
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Thanks guys. Must admit, I'm more inclined toward the 4-stroke 20hp option than the 25hp 2-stroke, so good to hear your experience with a 20hp on a loaded 3.9 RIB, Polwart.

Howver, I guess it's a case now of seeing what I can find within my budget.

I'd still appreciate any recommendations on good sources for used motors. Cheers!
Just realised you are talking RIB not SIB here. I'm sure you'll still get on the plane (I have an oddball boat that is neither but does have a rigid reasonable v-hull but lighter that a typical RIB).
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Old 25 October 2009, 16:22   #7
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As well as the usual suspect you have listed, Fairweather Marine in Fareham usually have a few 2nd hand outboards for sale:

http://www.fairweathermarine.co.uk/

I have always found them very helpful.

Ron Hale in Portsmouth usually have a few:

http://www.ronhalemarine.co.uk/super...Used_Outboards

I've never used them, possibly a bit pricey?

Also try Home Marine in Emsworth, I have bought a few things from them and again found them very helpful:

http://www.emsworth-marina.co.uk/Services.htm

Finally, I bought my outboard new from Pacer Marine, at a good discount:

http://www.pacermarine.co.uk/NO-CARTgallery1.htm

Cheers

Chris
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Old 26 October 2009, 06:52   #8
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Other plus side to the 4- stroke if you aren't bothereda bout flat out top sped is the 4- stroke will likely be quieter & more frugal at lower rpms.

If you get the prop pitch right planing should be no problem.

I had no issues with a Suzi DT25 on an Avon SR4. Said engine may be available soon, depending what happens with the Merc rebuild! (i.e once I know for sure that it's not going to be needed for more "standby duty" while I look for a replacement 60)
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Old 26 October 2009, 09:46   #9
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A mate runs a 20 Honda on a 3.5 & regularly does 20 mile runs to the Isle of Wight & back - so reckon you wil be fine. You wont be going super quick , but I think will plane quite happily as I think the hulls are quite flat so will plane with a lower HP than say an SR4 .
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Old 27 October 2009, 04:30   #10
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Thank you all for your comments. Much appreciated.
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Old 17 November 2009, 13:09   #11
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I don't know if I can agree with that advice.

I have that exact same RIB -- Avon 340 -- which I use as a tender for a large sailing yacht. It has a Mariner 25 horsepower 2-stroke and jocky console. It planes happily and efficiently with up to about four people and no gear, but beyond that load it starts to struggle. With five adults and some stuff it will not plane.

I would not want less than 25 horsepower, myself, on that boat. It's a real plodder when not planing.

2-stroke or 4-stroke is a matter of taste, but I like 2-strokes myself, for their unbeatable power to weight ratio, and simplicity. You give up something on economy and perhaps longevity; these will be bigger issues if you use your RIB for any kind of continuous duty. For a tender it's not a big problem. The Mariner is quite quiet; I don't know about other 2-strokes.
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Old 18 November 2009, 04:29   #12
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Id defiantly go for the 25 2 Stroke, Had a Mercury 25 2 Stroke on my old rib - Valiant 3.80

Did about 27 knots!
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Old 06 May 2013, 08:37   #13
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Hi, I realise this is an old posting, but just joined the forum and I am considering getting a new Zodiac Cadet 340 RIB with trailer. So wondering about outboard options. Suzuki 20hp was recommended but wondering about 4 stroke vs 2 stroke and possibly going for smaller 15 hp and not necessarily Suzuki. Having seen your discussion from 2009 I'm guessing you now know what worked for you. Any thoughts that might help me in my decision?
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Old 07 May 2013, 01:49   #14
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even if you go for 20hp, I would still look for a 2 stroke! I think for smaller crafts the advantages outweigh the disadvantages. My 25hp 2 stroke is fine on fuel and I was surprised I.e. pulled a knee boarder for 1 hour and a half at 3/4 throttle and I only used a few liters.

With the 2 stroke you will have more talk so will be able to take a bigger load, you will have better acceleration, better top end speed. Once you got your wind in the hair flying along at 30 knots (one person on board) you won't even notice the extra noise
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Old 08 May 2013, 03:49   #15
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Everything else aside, on a "small" boat weight distribution is crucial, and the extra Kg will be noticed. Alsio should you decide not to use the trailer the extrra weight will be noticed when lugging the engine around, and 4- strokes are more fussy as to how you lay them down in the back of the car......

Two reasons to actively go 4- stroke. If you do a lot of "pottering" / fishing the 4 will drink less at low RPM, and will be a, lot quieter. If you spend the time razzing about with a wide open throttle, chances are the difference will be negligible.
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Old 08 May 2013, 04:05   #16
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I originally fitted a Tohatsu 18hp 4-stroke, but later upgraded to a Suzuki DF25 as the 18 struggled to push the boat over the 'hump' with two or more aboard. The 25 made a big difference, and fuel usage actually dropped as it would happily hold on the plane at lower revs than had been needed with the Tohatsu.

Personally I preferred 4-stroke over 2 for the reduction in noise and exhaust fumes, though I accept that a 2-stroke may well have improved the ability to get on the plane and the weight distribution. The Avon had a power and weight limit for the transom so worth checking whether the same is true for the Zodiac Cadet as this may restrict your choice.
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Old 08 May 2013, 04:47   #17
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Thanks for the advice. It has helped to narrow down choices, so currently thinking I'll go for the new Suzuki 20hp 4-stroke at 44kg. Max allowed is 25hp, max recommended is 20hp.
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Old 08 May 2013, 13:11   #18
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Thanks for the advice. It has helped to narrow down choices, so currently thinking I'll go for the new Suzuki 20hp 4-stroke at 44kg. Max allowed is 25hp, max recommended is 20hp.
If you can afford a 25hp I'd go for it. It is heavier than the 20hp, but won't increase overall laden weight (boat + engine + crew) by the 20% that you'll be gaining in power, and it's costly to buy a 20 and then wish you'd gone for the 25 (which is effectively what I did).
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