What hp needed to power a 2.7m RIB?

richardjawilson · 19 January 2011, 19:06

Hi there, I have a 2.7m rib tender, used to access the bigger rib when its on a swinging mooring on the Dart.

The tender is a Tidalwave one, cheap but does the job, boat only weight is about 55 kgs, rated to 9.9hp with payload inc motor of about 315kgs, so 3 adults.

Its currently/temporarily powered by a 4hp 2 stroke Mariner Sailmate but that's a longshaft and has a prop for suited to heavier boat. It digs the stern in when underway and with 2 up, it can't overcome the extra drag of the leg so does not plane (4hp with 2 up may not be enough anyway to make it plane even with an s/shaft).

I am thinking of a S/shaft 6hp or a 9.9hp, but I am concerned about the weight of the 9.9 over the 6. The 8 hp's seem to weigh the same as 9.9's, so I've ruled that engine size out.

Any thoughts??

Thanks Richard

ps,

Budget not too much of an issue.
The new or s/hand engine may also double as aux on a 6m rib.
More than happy with a 2 or 4 stroke but favouring 4.

achille2124 · 19 January 2011, 19:24

First thing do not try to raise the transom to use a long shaft outboard on a short shaft application. I've tried it before on a 3,10m RIB and I almost flipped the boat the first time I floored it, very dangerous.

With a short shaft 4 hp you should be able to plane (in calm water) by distributing the weight in the boat, however I don't know the brand & model of your boat so it might not be true. On a Cadet RIB 260 with a 4 stroke Yamaha I got it to plane real easy.

My suggestion is to get a Yamaha 2 stroke 8hp short shaft. I don't know if 2 strokes are still available in UK but here in Canada this model is very popular. The Yamaha 2 stroke 8hp weights only 60 pounds, wich is the same as the 4 stroke 4hp and 6hp.

With a 8hp, you'll not only plane in an instant but it will be a reasonnable auxiliary for your bigger RIB.

Cheers!

willk · 19 January 2011, 22:04

Intestesting. I asked this question here recently for my 2.7 air deck. The answer was basically the Yammie 8hp 2T or a Tohatsu 9.8hp 2T. They weigh much the same at 26kg ONO.

I went Tohatsu and the trial run was more fun than a barrel of monkeys.

richardjawilson · 20 January 2011, 09:05

9.8 Tohatsu sounds great but where can I buy one? I guess I need to wait for one the crop up on ebay etc.

willk · 20 January 2011, 09:20

They crop up now and then. I've seen three since September. They're not getting any cheaper, or younger!

Clicky

9D280 · 20 January 2011, 12:09

Or get a cheap & cheerful 2/4 Hp short shaft & bring the rib back to the pier / slip to pick the rest of the crew up?

richardjawilson · 20 January 2011, 17:59

4/6 hp would work. I was looking at a new Yamaha 6 hp which would be great but the tohatsu 2 stroke is the same weight so would by that if I could.

Oh well I'm bid here for a tohatsu if anyone has anything.

spartacus · 22 January 2011, 09:42

Quote:

Originally Posted by richardjawilson

4/6 hp would work. I was looking at a new Yamaha 6 hp which would be great but the tohatsu 2 stroke is the same weight so would by that if I could.

Oh well I'm bid here for a tohatsu if anyone has anything.

As luck would have it. (I don't know seller).
http://www.findafishingboat.com/tohatsu-9-8/DS29575

spartacus · 23 January 2011, 10:24

A few hours to go. Looks mint.

http://cgi.ebay.co.uk/tohatsu-9-8-hp...#ht_572wt_1141

richardjawilson · 23 January 2011, 11:38

have seen that one, but its a 4 stroke. Good value though, but heavy at 37 kgs. I am tempted but its the weight thing.