What speed for my new RIB?

[Colin Barbados]

Hello all,
Frist time post – Just bought an ‘AB Inflatables 13 foot RIB (VS13) and a Mercury 40hp EFI 4 stroke. I’ve not had a go in it yet as I’m waiting for the small center console, wheel, and controls to be fitted.
As you can imagine, I’m bursting to get it in the water. I keep it in Barbados and it will be used just for leisure and hopping between the beach bars on the west coast. Up until now I have been hiring a slightly smaller (12 foot) AB rib fitted with a 25hp motor. I won’t be back in Barbados until late June, but by then my Rib will be ready to use.
No doubt I’ll be posting questions to pick the brains of the more experienced forum members over the next couple of weeks, but I’ll get the dumbest one out of the way now… How fast (very roughly) do you think it will go (flat out / and practical cruising)
Cheers
Colin

[Exe treme]

Wow. Thats a lot of power and weight for a 13 ft rib, but there are others that can handle the same and I believe AB make good ribs. There are lots of considerations like prop pitch, max hull design speed, boat weight etc, etc, which is possibly why you haven't had any response. A friend of mine has a similar size with a Tohatsu 40 2-st but he gets scared at 27 mph, so not sure of w.o.t speed. Expect easy cruising at 20-25 mph and w.o.t. in excess of 30-35 mph if set up correctly, and if you are brave enough as it might feel like it is going to take off! I am no expert but thought I would respond as nothing else has been posted.

[Colin Barbados]

Originally Posted by Exe treme

Wow. Thats a lot of power and weight for a 13 ft rib, but there are others that can handle the same and I believe AB make good ribs. There are lots of considerations like prop pitch, max hull design speed, boat weight etc, etc, which is possibly why you haven't had any response. A friend of mine has a similar size with a Tohatsu 40 2-st but he gets scared at 27 mph, so not sure of w.o.t speed. Expect easy cruising at 20-25 mph and w.o.t. in excess of 30-35 mph if set up correctly, and if you are brave enough as it might feel like it is going to take off! I am no expert but thought I would respond as nothing else has been posted.

Many thanks for the reply Exe,
That will give me a starting point. I don’t know the pitch of the prop yet. The dealership who have sold me the engine have visited the boat in order to choose the best pitch for its size and shape. I agree a 40hp 4 stoke is a big lump for a tiny rib, but the very similar rib I’ve been hiring up to now had a 25hp attached and left me thinking I’d like just a bit more. A 30hp was considered, but at only 5 more horses seemed too small an increase. Buying a brand new outboard is a big investment for me and I didn’t want to commit to a 30hp and soon be wishing I’d got for the 40.
The plate on the RIB says 40hp max and the weight is within spec. The Rib seems very workman like and strongly built. The 13” VS AB Rib (Navigo range) does not come as standard with a factory fitted center console, but is an open tender with a tiller grip outboard. The console will move my weight more forward and will help the balance fore and aft.
I’ve noticed that a lot of the posters tend to speak about MPH instead of knots, is this a RIB thing?
A cruising speed of 15 to 18 knots will be just perfect and anything approaching 27 knots WOT would be fine to put a bit of wind through my non-existent hair. I have many years of experience driving much more powerful small craft… workboats and fast rescue craft in the off-shore industry, but they have all been jets, I know diddly squat about low powered props. Lots more dumb questions to follow.
Cheers
Colin

[Poly]

Possibly fast enough to scare the **** out of most people who might be driving it! I get 22 knots out of a similar sized boat with a 20HP 2str and it feels like driving a go-cart. I'd take it easy to start with and make sure you have a life jacket and kill cord on. If it starts chine walking it could flip you out!

[9D280]

Colin,

Hi, your post must have been eclipesd by one I had seen already. Welcome to the madhouse!

Cruising wise most ribs of that size seem to go "nicely" with best fuel effy between 20- 25 knots. FWIW I have a 60HP on a 5m (16') and the difference between 22 & 28 knots is quite a step change in concentration & hard work.

Sounds like you might have a bit of fun with that!

[Colin Barbados]

Originally Posted by 9D280

Colin,

Hi, your post must have been eclipesd by one I had seen already. Welcome to the madhouse!

Cruising wise most ribs of that size seem to go "nicely" with best fuel effy between 20- 25 knots. FWIW I have a 60HP on a 5m (16') and the difference between 22 & 28 knots is quite a step change in concentration & hard work.

Sounds like you might have a bit of fun with that!

Poly, Many thanks for the advice; a kill cord is a given. I’ll certainly be taking it steady until I get a feel for how this particular combination of boat / engine reacts to the sea state.
9D280, Thanks for the welcome. “Nicely” at 20 – 25 knots would be perfect. Fuel efficiency may be important. There is a fuel dock a couple of hundred meters for where I keep her at Port St Charles, most of the destination beaches are between 2 and 8 miles run (one way) from there.
I would like to be able to get to Bridgetown and back (with a comfortable reserve in hand) Bridgetown would be a 28 mile round trip. Does that sound doable on a single tank? I’m assuming the tank that arrives with the engine will be 22 ltr.
Any thoughts…

[9D280]

As a going in guess and until you get some "hard data" (even if you stick a handheld GPS in your pocket!), assume 1L/ mile. Onthe first few trips it's worth making regular checks of the tank (like pick it up or look in the filler - don't rely on those useless built in fuel guages!).

I've kept a note of fuel / dist / sea state / driving style data since I rebuilt my engine, and so I am now a lot more confident about predicting useage knowing the planned activity / weather forecast.

Portable tanks are cheap. It's prrobably worth buying another and using them turn about (stops the fuel in #2 going stale). Also means if for some reason you get water in one, you can swap & get back.