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Old 06 November 2016, 15:54   #11
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70hp on an Avon SR4?

Hi Alex,

Was that the boat that was on eBay?

I don't know the weight of your 70 but I had a yam 55 on mine for a couple of years and with everything heavy forward it was pretty well balanced and that was one heavy lump!!

Have to agree with the others though. They are awesome boats but a little hairy after 30 odd knots and a 70 is going to push it VERY fast. As mentioned above they chine walk a bit in certain conditions and a fast stern heavy setup is going to make that worse . Use it sensibly and I think it will go ok and have awesome acceleration, and if it was mine I would try it out see how it goes and keep an eye out for 50. It wouldn't cost much to trade in your 70 for a nice yamaha 40 or 50. I know it is the cliche combo for the SR4 but now having finally got a 50 with ptt I can see why.

I think someone had a 60 on one few years ago but can't remember who or how it went? Think they ended up with trim tabs though to make more stable
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Old 06 November 2016, 17:13   #12
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Old 06 November 2016, 20:11   #13
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Yep, I wouldn't either. My SR4 hit warp speed with a 50hp. You don't need 70hp, it's way too heavy and too much for the transom.

Besides, it'll drink fuel for no usable extra performance.
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Old 07 November 2016, 01:20   #14
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Hi there again, thanks for all your posts, sorry for my sharp response, as regards to my rib i know 70hp is a bit much, weight wise it's about the same as a yam 50hp 4 stroke, mines probably got less hp than the 70hp, still doing some work on the boat before it goes on the water, see how it handles? was planning to take it safe, i will take your advice on looking out for a 40/50hp (any help there would be great) - either sell my set up (runs well for an old un) or keep on to it for my next (larger!) rib, again thanks again for your help, alex
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Old 07 November 2016, 01:51   #15
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Originally Posted by Alex r View Post
Hi there again, thanks for all your posts, sorry for my sharp response, as regards to my rib i know 70hp is a bit much, weight wise it's about the same as a yam 50hp 4 stroke, mines probably got less hp than the 70hp, still doing some work on the boat before it goes on the water, see how it handles? was planning to take it safe, i will take your advice on looking out for a 40/50hp (any help there would be great) - either sell my set up (runs well for an old un) or keep on to it for my next (larger!) rib, again thanks again for your help, alex


As long as its not over the manufacturers maximum recommendation I would go with as much power as possible, you don't have to use it all. If outside the manufacturers max you could end up in trouble if an accident happens and someone gets injured.

Being able to run at lower rpm and still maintain good cruise speed will be far better on the fuel consumption.

If you carry heavy loads such as a few mates and dive gear like I do and have to cross bar crossings which are often extremely dangerous then the more power you have to sit on the shoulder of a big wave the better. Power can be your best friend working big seas. If you look at the swell in this shot in-front of our river entrance you will note a solid 2.5m swell with almost flat conditions once you pass the shore break. Trying to cross these bars without enough power brings many a boater undone.

If you find its to much power theres quite a demand over on the worldseafishing forum (UK) for engines around the 70hp.

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Old 07 November 2016, 03:20   #16
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As long as its not over the manufacturers maximum recommendation I would go with as much power as possible, you don't have to use it all. If outside the manufacturers max you could end up in trouble if an accident happens and someone gets injured.
SR4 is rated for 50hp, AFAIK?
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Old 07 November 2016, 03:26   #17
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Ok, any idea's for a 50hp, best places to look? Price's etc
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Old 07 November 2016, 03:46   #18
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Ok, any idea's for a 50hp, best places to look? Price's etc
Couple of 50hp engines here:

2005 Tohatsu long-shaft 2-stroke
Tohatsu - M50D2 3E3 Boat Engines for sale in Devon, South West | Boats and Outboards

Mid 90s Yamaha long-shaft 50hp, power-trim
https://www.gumtree.com/p/boats-kaya...ed./1197813516
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Old 07 November 2016, 05:39   #19
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Weight and power wise a Yam 55 will be cool too. I'm running one on my SR4 with no problems concerning speed and seakeeping.
I've increased the thickness of my boats transom when I re-did all the wood though. A friend of mine owns an original 4M, with a 50HP engine as well, and his transom flexes slightly during sharp acceleration.

All Seariders like light engines more than heavy ones., weight limit is 110 KGS on the 4m, but that much weight will upset the balance and make the boat handle less than optimal.
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Old 07 November 2016, 06:13   #20
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What would be the optimum transom thickness required for a 50hp +engine, thanks alex
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