Ribcraft 6m ride problems

IanMcDean · 26 August 2008, 11:36

Hi,
My dive club bought a 6m ribcraft new last year, I belive this was a boat built using the 6.8m mould but shorter. We initialy found that the boat was under powered having speced twin 50Hp honda's. We solved this by replacing with a single 150 optimax however we are now finding that she is extremly uncomfortable to use due to her not being able to plane till about 18kts and when she does realy slams into the waves to the point where its dangerous (due to the heavy kit onboard). We have an old Humber dive pro which is great and comfortable to use in the same conditions.

So any thought as to why this is the case? We think this is function of the hull being very wide and deep v'd for the length of the boat and the amount of chines on the hull causing it to slam for violently.

Im not an boat engineer by along way but would appreciate any feedback on how hull shapes effect ride and performance.

thanks

Ian

Simon B · 26 August 2008, 12:04

Interesting, this was on my list of possible dive club boats for the replacement of our Delta. I'd been looking at the 6.4 Ribracft or the 6.3 Humber Destroyer.

We arent sure about the clubs ability to tow and launch the larger sizes with a "normal" aka Mondeoman car. However, as a 6.0 metre boat would probably need a 150 in terms of wieght it would be pretty close to a 6.3/4 with a 175 (probably same engine block etc)

Not planing till 18 knots sounds a bit strange, is the wieght distribution ok? Its almost as if the boat is ploughing with a motor that might not be propped correctly. What rpm do you get at wide open throttle?

codprawn · 26 August 2008, 13:42

Sounds like it could be a rigging problem or you need trim tabs - or both!!!

I suppose it's possible the design could be bad but Ribcraft have a very good name - what do they say about it?

PeterM · 26 August 2008, 14:20

Agree with Cod - I have always, & only ever heard good things about Ribcraft handling & had good personal experiances. Could it be a very stern heavy setup giving very high planing speed ?

Have you tried running it with differing weight distributions - ie load up front etc ?

matt h · 26 August 2008, 15:27

saw this boat, its a one off, pm sent

Bigmuz7 · 26 August 2008, 16:39

Ian ... Do you mean slams left then right without warning or just generally into waves ahead ?.. Also, could any water be trapped in the hull at all ?

IanMcDean · 27 August 2008, 14:36

Hi,
thanks for the replies so far good stuff (apart from there seeming to be no simple answer). By slamming i mean it basicly goes through the wavesand when going over realy slams back downhard. It may be stearn heavy and we have tried getting people as far forwards as possible but it doesnt help. Maybe we do try trim tabs??? It is proped right we get the right engine performance it just doesnt work right on the plane and getting to the plane...

thanks

Ian

Andy Gee · 27 August 2008, 14:54

How many divers are you carrying and what kit?
Andy

Jon Brooks · 27 August 2008, 15:38

To go back to what someone else asked............

"what have Ribcraft said?"

IMHO they built the boat, they know the boat thus would be far better to ask them rather than those of us on here that, mainly, just drive them and not build them.

I would ask was it doing it prior to the re-engine?
If it is back heavy, could this be the case of wrong engine and or to much kit at the rear?
Who fitted the new lump?
Was it fitted correctly?

If she is taking to long to plane them maybe to much kit etc.

Like others have said, the Ribcraft is a very good brand and not many that have troubles with them and most deff worth a call to Dorian or Charlie down there for some "expert" advice.

All the best

Pete7 · 27 August 2008, 16:21

Quote:

Originally Posted by Jon Brooks

IMHO they built the boat, they know the boat thus would be far better to ask them rather than those of us on here that, mainly, just drive them and not build them.

Or have spent 20 years diving from ribs and remember Ribcraft as a one man band when they first started and turned them down because they built a hull too heavy which meant carrying less divers than other makes.

Pete

Simon B · 27 August 2008, 17:32

Quote:

Originally Posted by IanMcDean

Hi,
By slamming i mean it basicly goes through the wavesand when going over realy slams back downhard. It may be stearn heavy and we have tried getting people as far forwards as possible but it doesnt help..... It is proped right we get the right engine performance it just doesnt work right on the plane and getting to the plane...

Our Delta did very similar things, I think it's typical of a boat that is;

very deep vee
stern heavy (take a critical look at how she lies in water)
possibly lacks the torque to climb onto the plane quickly

Try trimming all the way in (ploughing) when you start, this goes some way to lift a heavy stern
Lifting foils on engine (cheaper option than trim tabs)
Modify driving technique radically.

Last point is basically to try and prevent the boat flying off the top of a wave, the stern (in a stern heavy boat) would normally fall away dramatically.
I think our boat is slightly underpowered and it doesnt take much to knock it off the plane if you dont judge the conditions right, it then takes some time to regain speed and go onto plane.