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Old 13 May 2008, 17:01   #21
Country: UK - Wales
Town: swansea
Boat name: Too Blue
Length: 8m +
Engine: Suzuki DT225
Join Date: Mar 2004
Posts: 12,791
I still think the tubes may be twisting - as the stern drops the tubes roll up slightly allowing the water level to rise. If this is the case it may be the way the tubes are attached.

codprawn is offline   Reply With Quote
Old 13 May 2008, 20:57   #22
Country: USA
Town: Fort Myers Florida
Boat name: Bastard for now
Make: HBI
Length: 4m +
Engine: 50 horse evinrude
Join Date: May 2008
Posts: 16
Originally Posted by codprawn View Post
I still think the tubes may be twisting - as the stern drops the tubes roll up slightly allowing the water level to rise. If this is the case it may be the way the tubes are attached.
They are the type of tubes that you can slide on and off (i have never done this)... i can lift up on the tube when fully inflated and it moves. What do you suggest i do to test your theory "Cod"?

mlynch is offline   Reply With Quote
Old 14 May 2008, 10:50   #23
Country: USA
Town: Seattle
Boat name: Water Dog
Make: Polaris
Length: 4m +
Engine: Yamaha 60hp
Join Date: Apr 2007
Posts: 1,152
Originally Posted by Pete7 View Post
Matt, those figures are about right, but I think you're asking to much from a little rib and small engine. We used to dive off a Humber Alpha (4.9m) of similar size with a 55 hp mariner. Cruising speed with 4 divers and kit was 20 knots and about 26 knots empty. However other than the engine and two 5 gallon tanks of fuel there was very little furniture in the boat. Even the steering console was a simple stand up light weight affair.

If you want to use it for diving you are going to have to ditch the canopy frame and seats. That engine lift isn't doing anything for you either. Manual engines normally have a gas assist strut to help lift them up, why doesn't it work? I would have thought as a diver you could lift a 50 hp up no problem. Bottom line is you need to strip the boat of anything that isn't essential including seats, canopy frame and large amounts of petrol. Then move the stand up steering console further forward to create deck space for diving and keep the weight forward. All this will save the weight and give room for the dive kit and getting kitted up.

Agree, there's no way a 50hp is going to push all that crap at 40knts. Even 30 would be a huge surprise to me. I have a 15.5ft Ali RIB with a fairly flat deadrise (compared to some - its 15deg). It's lighter than a GRP boat at about 480lbs. Even with that flatness and lighter weight helping my speed, my 60hp Yamaha "only" gets me to 30knots empty on flat water. 4 divers aboard I max out around 26 knts.

I would guess you real max (empty) speed with that 50hp is more like 28knts:
The T-top is killing 3 to 4 off that.
The engine bracket maybe 2.
The water inside 3 or 4 more.
Net Max is hence 20ish.

You either need to strip off the superfluous gear, or get a bigger engine if you have your heart set on speed.
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Old 14 May 2008, 11:36   #24
Country: Other
Town: San Carlos, Mexico
Boat name: INDE
Make: LOMAC 730
Length: 7m +
Engine: 200 Merc.
MMSI: Please press 1
Join Date: May 2006
Posts: 1,688
Send a message via Skype™ to Limey Linda
If you decide to remove the T top maybe I could use it on my 24 footer; depending apon dimensions. PM me if you are interested. I agree with everyone else, you boat is overloaded and adding a bigger engine is not going to help to much for diving purposes, just more weight and lower in the water.
Best of luck

Running around like a head with it's chicken cut off.
Limey Linda is offline   Reply With Quote

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