Print

Please login or register.

[scgunner]

rmjohns, pbyrne,

If you're getting no RPM increase after 80% throttle I'd say you've either already hit the stop or the control is not opening throttle to the max. Changing the prop may get you some more RPMs at the top end but it will most likely cost you some bottom end torque. It's the torque or low end grunt that gets you moving and up on a plane not the prop or the HP.

I'd say the reason Ron can more easily get on a plane is his 2-stroke weighs significantly less than your 4-stroke and that weight is concentrated on the very back of the dinghy. Imagine trying to get on a plane while sitting on your motor, then trying it while you are hanging over the bow, which way would the dinghy more easily achieve a plane.

Unfortunately the only way to increase torque is with a bigger (aka heavier) motor. One other option would be to lighten the overall dinghy package which will have the same effect as a torque increase.

[Ron Hill]

Guys : Beside crew weight and 2 vrs. 4 cycle (weight again) a VERY big difference is having a 8' RIB (short - weigh once more/less surface friction).  The bottom is hard and I put a coat of wax so it's as "slippery" as it can get (reduced drag/friction)!!

A few thoughts

 

[scgunner]

Ron,

FYI, I used to work with a guy who was a nationally ranked Hobie Cat racer when I asked him about bottom prep he said the last thing you want to do is wax the bottom, it creates a suction that causes drag and actually slows the boat down. He said if you want to go fast wet sand the bottom with 400 wet/dry that's what makes the bottom slippery. However for a working dinghy a protective coat of wax is probably a good idea.

[Noah]

Then on the flip-side… is my 2001 hypalon Avon Rover roll-up with aluminum slat floor and 2 hp. air cooled Honda 4 stroke—which serves me well. Taking a chapter from the “tortoise and the Hare” 

[scgunner]

Noah,

My original setup was a Cribe 10' RIB with a 15hp Merc 2-stroke which I used as a dive platform. This arrangement would transport two divers, two sets of dive gear and two extra tanks at around 17 to 18 knots which was great for getting quickly to and from distant dive spots.

The problem was while it also works great for to and from the dinghy dock and dinghy cruises the setup when not diving is a real mother, that Merc weighs 70lbs and it's big which also makes storage a challenge. So I did what you did I got a Honda 2.3hp 4-stoke. It's great, it's lightweight, stores easily in the port side cockpit locker, doesn't need pre-mix and easily gets us to the dock.

[pbyrne]

Noah,

My original setup was a Cribe 10' RIB with a 15hp Merc 2-stroke which I used as a dive platform. This arrangement would transport two divers, two sets of dive gear and two extra tanks at around 17 to 18 knots which was great for getting quickly to and from distant dive spots.

The problem was while it also works great for to and from the dinghy dock and dinghy cruises the setup when not diving is a real mother, that Merc weighs 70lbs and it's big which also makes storage a challenge. So I did what you did I got a Honda 2.3hp 4-stoke. It's great, it's lightweight, stores easily in the port side cockpit locker, doesn't need pre-mix and easily gets us to the dock.

Yeah, the 6hp is plenty big enough to manhandle.  I can't imagine what a 15hp would feel like!  If electrice wasn't so mind boggling expensive I would have gone with that.