Laden dive boat...prop change?

[Razorbill RIBs]

We've been experimenting with loading up with lots of media /dive gear for a potential project we've got coming up. We'd need to carry a lot of spare dive gear for a series of dives.

The Ocean is a heavy old lump of a boat and not a fast hull by any means, but she achieves 40 knotts with the 150 Opti running a 19 prop.....more than enough for us!

Have run previously with heavy kit (media divers) and 6 up and whilst not spritely, have achieve around 27 knotts....happy with that too.....

For the project we would potentially need to be loaded up for 4 dives (Everyone diving twinsets) with 6 divers and 1 or poss. 2 crew.....so lots of kit, additional air etc....lots of big blokes too....we'd also be carrying additional fuel (over the 32 gallons in board).

Having loaded up with the same sort of weight we went for a trail run, but just couldn't get the boat to plane properly no matter where the weight was distributed and made around 12 knotts and max 3,500rpm.....time to rethink!

So, am i simply asking too much from the 150 Opti? OR might I have more joy if i try another (which?) prop specifically for when we are running with such heavy gear OR is there something else I could try....I don't want to run overweight /dangerously, but the sponsons were only just resting in the water at rest (usually float above), so confident the hull wasn't overloaded.....no need for great speed, but planeing would be nice

Not sure if it's relevant but the Transom is rated for max OB of 225....at this rate think we're going to need a second boat....

Any advice from divers /those in the know appreciated

Thanks,

Dan

[Chris]

Dan, sounds like you need to drop at least 2" in pitch and probably 4". You are seriously overpropped for the load you are carrying which will f**k the Opti very quickly. Imagine trying to drive you car everywhere in 5th gear. See if you can try a 15" prop to start with.

[willk]

Dan, I guess your rib has a max loading of circa a ton. That lading list sounds well in excess....

[Bigmuz7]

Thats a hell of a kit by the sounds of it .. on my 6.3 with an opti 150 we only ran at your similar speeds with 2 up .. with a full family and gear and a dingy strapped to the A frame I felt surprised as how quickly the power/speed dropped off ,.. but we ran a 21 for speed so a 19 would be normal for loads .. in your case maybe a 17 is the answer or perhaps a four blader 17 which will be cupped less

[chewy]

Does sound alot of weight, like willk said I'd find out what load it can take?

[willk]

Originally Posted by chewy

Does sound alot of weight, like willk said I'd find out what load it can take?

Having played around with the figures, I'm getting a potential load of 1500kg, which may be shiftable, prop-wise, but from an MCA point of view - tricky.

[Bigmuz7]

Originally Posted by willk

Having played around with the figures, I'm getting a potential load of 1500kg, which may be shiftable, prop-wise, but from an MCA point of view - tricky.

Thats closer .. mine was about 1550 but it depends how you have it rigged

[Razorbill RIBs]

Originally Posted by Bigmuz7

Thats closer .. mine was about 1550 but it depends how you have it rigged

Bigmuz /Willk....I reckon your weight calcs are probably right at the 1500 1550 kg mark....I have been trying to find out what the carrying capacity for the Ocean is, but struggling so far....will give Malcolm Winsor a call and see if he can advise....

The main reason for testing is that we would want to re-do our stability tests (MCA) with all the kit on board....

Chris /Bigmuz, will try and get hold of /try a 17 prop anyway.....as even with less gear, the additional hole shot would be useful.....would swap props for 'laden' and 'normal' running.

I am fast reaching the view that a second boat is the answer....it's just making the numbers stack up.....

Thanks for your helps with this, will let you know how the 17 works when I get hold of one....Anyone got a cheap coded RIB for pennies?

Dan

[GordyP]

Dan,

I use two sets of props on my rib, 21" for running around with only a few people on board and 17" for when we go out with 8 divers and full kit. I think the main problem you'll have from the sounds of things is just how busy the boat will be, getting kitted up won't be much fun.

Cheers.

[Simon B]

Talk to the nice lady at Steel developments prop repair she have a reasonable idea of what's about right. Think also about a 4 or 5 blade prop, if you really want to push the boat out think about stainless (original post did not mention this) but cost may be factor.

I would have expected an engine of that size to do the job if you are not exceeding the wweight and have your prop correct. It will not be a racing machine but a guess would be 27-30 knots on flat water. Whether you would want to drive a boat at that speed with the weight you have mentioned is purely up to skill and experience - how are you off for insurance?