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Old 27 February 2008, 13:05   #1
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25HP too little for 4.2m RIB?

if my RIB is titally open, no console, nothing, would a 25HP be enough considering that there will be 3-4 guys and moderate seas?
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Old 27 February 2008, 14:34   #2
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No. Unless you want to move at displacement speed all the time.
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Old 27 February 2008, 15:39   #3
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displacement speed? whats that, top speed?
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Old 27 February 2008, 15:55   #4
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25HP, In my opinion would not be enough. I have a 50HP on my 4.3 and when you think about a bench seat, or console, you are talking only a couple of hundred pounds. Which would equal to one person, and if I were to have a 25HP on the back, it would definitely be slow going.

So to have 3 or 4 guys and then try to get through some chop, it would not be be fun.

I would suggest a 40 HP two stroke.
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Old 27 February 2008, 15:57   #5
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if my RIB is titally open, no console, nothing, would a 25HP be enough considering that there will be 3-4 guys and moderate seas?
A client was using a Gommonautica 430 RIB with a Johnson's 25 HP 2 strokes, performed poorly al WOT, a Tohatsu demo 30 HP was placed, performed much better with 4 adult mates, but definitely a 40 HP would perform best.

If money is a issue, why not save some, try to get at least a Tohatsu 30 HP or a 40 C HP 2 strokes (Compact Version) weights 7 KG more (58 KG) and has 60 CC more (490 CC) compared to both 25/30 HP (52 KG/430 CC) standard Tohatsu models. Personally like to configurate larger sibs/ribs with the max engine they can tolerate. Generally speaking, trailer transported sibs/ribs.

Would be nice if you could find demo engines to test them, before a final purchase decision.

Happy Boating
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Old 27 February 2008, 15:59   #6
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far from it! displacement speed is speeds at which the boat moves by displacing water rather than planing across it. moving water uses lots of power and speeds are slow and uneconomical. planing uses less fuel and is more efficent. it needs less power to sustain a planing speed than to get there, with 4 up on rib that size you will struggle to get planing. bigger engine=less fuel wierd eh?
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Old 27 February 2008, 23:22   #7
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Thanks guys,
the other option would be to use the 25HP on a smaller RIB like a 3.6m, im just concerned that a 3.6m might be small for 3-4 guys, right?
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Old 28 February 2008, 06:16   #8
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My old SR4 went OK 2 up with a 25 on the back and a ton of wood as a console and 60L fuel.. I guess the water ballast was equivalent to at least one extra bod.

Granted, it wasn't spectacular hole shot, but it went OK.....
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Old 28 February 2008, 08:09   #9
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Thanks guys,
the other option would be to use the 25HP on a smaller RIB like a 3.6m, im just concerned that a 3.6m might be small for 3-4 guys, right?
360 & 380 Ribs would be much better with 25 HP, still confortable inside with 4 mates, happens that a 420-430 is a limousine size when completely empty(console, etc) Anyway you won't be going out with 4 all the time, so these sizes ribs will be perfect to match the engine already have.

Happy Boating
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Old 29 February 2008, 01:32   #10
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Thanks Loco and everyone, are these pics of a 4.2m with 30HP tohatsu? how does it perform with 4 guys on board...ill tell you my dilemna as i currently neither own the RIB or the ENGINE , but im looking for a very simple/hassle free (as much as possible) setup to go spearfishing (typically 2 people but up to 4 people)...my options are as follows:
1 - Buy a 4.2m RIB and install a 25 HP (which i ruled out after the feedback in this Thread)
2 - Buy a 4.2m and install a 40HP (my mate has a 40HP mercury that was almost never used but has been stored for the last 12 years or so)..which will be the cheaper option and provide comfortable room and power for what i need..problem with this option is that im worried that we get the engine working and all and then every weekend have trouble with it and i find myself having to pay $$$$ for a new 40HP as now ill be stuck with the 4.2m RIB

3 - Buy a brand new 3.6m RIB with a brand new 25HP, so will have good performance and easier to deal with in terms of beach launching/recovery was just concerned a bit about space and maybe if the sea gets a little rough will it be safe enough versus a 4.2...
this is the one but it will be totally open, no console or seats or anything..

what do you recommend?
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