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Old 06 December 2008, 10:31   #1
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Country: UK - Scotland
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Engine too big?

Hi guys,
Been reading the posts but cannot find an answer to my query.

I have a Avon Searider 4.7m rib. It had a Suzuki dt75 on it and I used to take 4 divers, 4 sets of kit and 4 spare cylinders. It had a 13X19 prop and it would plane and cruise at 20-25kts depending on sea conditions.
Anyway..... the Suzuki gearbox failed and it was always hard to start so I replaced it with a Honda BF75 f/s. I`ve had the rhib in the water and it runs fine although it only had 2 divers and 4 sets of kit.

My question is... Is this engine too heavy for this boat? And if so, is it therefore dangerous?

I know the engine is heavier than the Suzuki but what if I limited how much gear I carried would that make a difference? Or is the difference negligible?

Lots of questions I know, and maybe the answers are obvious, but they`re only easy if you`re in the know.

Any advice gratefully received.

Thanks in advance.
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Old 06 December 2008, 10:47   #2
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If you have a look on Avons website you should find the details for the max engine weight etc.

Welcome to the forum.
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Old 06 December 2008, 10:53   #3
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Quote:
Originally Posted by bazza View Post
I know the engine is heavier than the Suzuki but what if I limited how much gear I carried would that make a difference? Or is the difference negligible?
I am sure Nos/Doggypaddle/RogueWave or one of the other searider gurus will be able to provide some specific comments but its not the effect on "total load" you need to be worried about - but rather the weight on the transom and the fact that all that weight is right at the back upsetting the balance.

Just how heavy is the new engine? I am guessing something silly like 150 kg. Moving gear forward will help rather than taking gear out. In terms of transom damage it may depend as much on your driving style (and if you like to get airbourne) and how its supported on the trailer as anything else.
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Old 06 December 2008, 11:01   #4
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Country: UK - Scotland
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Boat name: rib tickler
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Length: 5m +
Engine: 150hp Optimax V6
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Thanks for the quick responses so far guys.

From what I can find the engine is 136kg. If it`s just the balance to worry about then we have plenty weight in the dive gear to move forward to couteract the engine. I try and not get "airborne" as this tends to have the gear bounce about, and at 2000ish a set I don`t think I`d be too popular.

I had a look at the Avon website but couldn`t find anything listed about my rhib. Maybe it is too old?

Any further advice appreciated.
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Old 06 December 2008, 11:16   #5
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RIBase
http://www.avon-workboats.com/page/sr47m

Doesn't state max engine weight. But they will have been designed for 2 strokes, so your honda may be too heavy. You could try ringing avon if nobody on here has the answer.

Edit: Just noticed the one in the photos looks like it has a Mariner 60 fourstroke, which weighs in at 120kg, so not far off your honda
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Old 06 December 2008, 11:20   #6
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Originally Posted by bazza View Post
I had a look at the Avon website but couldn`t find anything listed about my rhib. Maybe it is too old?
its here: http://www.avon-workboats.com/page/sr47m
no weight specced. max 70hp, but twin 30 4str's would be close to weight you have, so if it were me - use with common sense keep an eye on transom for cracks and fix/reinforce early...
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Old 06 December 2008, 11:23   #7
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Max engine weight forthe 5.4m is 170kg so its gonna be less than this.

You could try reinforcing the transom yourself for peace of mind?
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Old 06 December 2008, 11:32   #8
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Thanks again guys. I have already got a sheet of metal(which used to be a metal step in a factory) on the transom and the 4 bolts go through this as well as the transom but I will heed your advice and keep checking for cracks.

So far the advice seems in my favour. I was more worried about it being dangerous. I`m not one for wanting rescued by the RNLI for being a prat.
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Old 07 December 2008, 07:19   #9
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Doing more searching on the net I have found that there seems to be a contradiction in the weight of the Honda bf75. More sites seem to say it s dry weight is 163kg and not 136kg as I had previously found.(may have been a misprint on the site I found as it seems just 2 numbers are transposed).

I have emailed Avon to see what the max weight is for my Rhib and will see what they come back with.
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Old 07 December 2008, 07:53   #10
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I've got 115 KG on the back of a 4m adventure. I thought the searider were built tougher - so I reckon on a 4.7 youd get away with it as long as you are not going for 4 ft of air every other wave ! If its 136 defo - if its more you shoudl be oK with suitable extra support.
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