25HP too little for 4.2m RIB?

marwan · 27 February 2008, 18:05

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?

Nos4r2 · 27 February 2008, 19:34

No. Unless you want to move at displacement speed all the time.

marwan · 27 February 2008, 20:39

displacement speed? whats that, top speed?

PacificNWrib · 27 February 2008, 20:55

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.

Locozodiac · 27 February 2008, 20:57

Quote:

Originally Posted by marwan

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

doggypaddle · 27 February 2008, 20:59

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?

marwan · 28 February 2008, 04:22

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?

9D280 · 28 February 2008, 11:16

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.....

Locozodiac · 28 February 2008, 13:09

Quote:

Originally Posted by marwan

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

marwan · 29 February 2008, 06:32

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?

Pablo · 29 February 2008, 10:39

Last year I did most of my spearfishing 2 or 3 up in a 4.2m Zodiac System Pro with a 40hp Yamaha. Admittedly the prop was very mangled but it used alot more fuel and struggled more when there were three of us. For spearfishing with the fins, weight belts, guns, fish, etc... I would suggest not having a console and using a tiller steer. How far offshore are you planing on going? Do you have very hot weather which will require an icebox?

We tend to take 3 guns each because the conditions and fish behaviour change alot. Are you planning on taking so many?

All this is to be taken into consideration.

marwan · 29 February 2008, 18:58

Pablo,
youre right and i am not even considering a console to maximize space, just the engine with tiller..normally we are only 2 guys, but on occasion we could be 3..the plan is to be geared up before we head out to the reef, the distance is not too far (1 -2 NM) and nothing offshore...
yes we do pack an icebox..but nothing massive as the fish in this area are in the 2-10Kg range most of the time..also typically just one speargun per person, maybe 2 at most
i was also thinking f making a small A-frame on the back where i can hang spearguns to save space and maybe try and install some sort of shade...
looks like im more inclined to the 3.6m with 25 HP at this point, what do you think, its like the one in the pictures

captnjack · 29 February 2008, 20:18

I had a 12.5ft Bombard (soft bottom, 3.8m) with a 25hp electric start Yamaha and it worked quite nicely for 2 or 3 divers. 4 in a real pinch. Max speed was good, planing speeds were good, hole shot pretty good. Biggest drawback to the smaller boat was rough weather performance. That was definately iffy. I was taking it up to 10nm each way (althogh not that far from shore). So the choice between 3 and 4m realy comes down to weather. What conditions are you going to want to use it in etc.

marwan · 29 February 2008, 20:39

i will be using it in mostly calm seas, sometimes it will get a little choppy but nothing too serious, other times it could get really rough in which case i just dont go out

thanks Capn Jack

captnjack · 29 February 2008, 20:48

I said the same things! The small boat without much in the way of electronics and such was super easy to keep up. Just spray it down afterwards and fill it up with fuel. Change the oil once a yr or so. Done.

But eventually I got sick of always being somewhat marginal on the weather issues. So I bought a 15.5ft (4.7m) ali hulled RIB. The combination of a rigid hull, longer length and bigger engine (60hp) makes alot bigger difference that a mere 1.5m might suggest. Now I'm hauling 4 divers, 8 tanks, dive propulsion stuff (scooters), have a VHF, and I'm cruising at about the same speeds that I used to max out my previous boat in totally flat water with (~22 knots). My range is also much much further. Like 15 to 25 nm each way from the ramp is plausible (although not that far offshore).

Cost me quite a bit more and takes alot more maintenance time too though.

marwan · 02 March 2008, 11:03

i used to have a 4.8m RIB with 60HP, bimini top, console, a-frame, the works, but got tired of maintenance and if im alone, i would be lazy launching it from the ramp...
now it boils down to either the 3.6m with 25 HP or the 4.2m with 40 HP, in bother cases, open and no console or anything....
deep down i know the 4.2 will be better for me and more comfortable in terms of space and rougher water, if i were to set price issues aside, the drawback versus the 3.6 could possibly be ease of launching and retreiving from the beach? i dont know how much the wight difference will be, between the 3.6m hull and the 4.2m hull, the difference in Engine weight between the 25 and 40HP is about 15Kg...

Pablo · 03 March 2008, 10:27

In that case I would say 4.2m with 25hp will suffice. 40hp would obviously be better. I've been out alot in a 35 year 4m rib (PB Marine for those in know) with an old 25hp 2-stroke Suzuki motor. With that boat we go out all year round and go to islands that are 10 NM from the coast.

You'll appreciate the extra length. The length is more important than the power in my opinion. But expect to cruise at less than 20 knots.

Locozodiac · 03 March 2008, 17:40

Look for a nice 380 with a 25 HP, 380 is more roomy than 360, use both and can tell/feel the boating difference. Other nice option a 4.00/4.20 with a 30 HP engine. For few (2-3) diving mates & gear a 380 will be perfect.

Happy Boating

marwan · 03 March 2008, 18:03

man! finding a wife was easier then this

really guys thanks for all the help...
loco, the options available locally are either 3.6 or 4.2, which i would rather stick to versus importing a RIB etc.. would cost much more...
i think i will go with the 4.2, seeing that in most cases we are really 2 people and on rare occasion maybe 3 or 4, also the seas are relatively calmer in the area i intend to use it..but again on occasion could be a bit rougher...
the 4.2 m will give me the comfort of space and maybe more piece of mind in case we need to go further etc... i also think the 25HP will work under these conditions, i will also check on prices/availability of 40HP if its slightly more expensive ill go for it, if not i think ill stick with the 25HP 2T...how does that sound guys..

tinker · 03 March 2008, 18:48

I owned a zodiac pro 4.2m with a big foot 25hp mercury 4 stroke(very heavy) center console and 25l fuel, with 3 * 14 stone men it made about 20-22 mph, would plane at around 15 mph, aint going to break no speed records but cheap on fuel