Performance expectations for 11' dinghy and 9.5hp

[Joe5.0]

So I just got my Quicksilver 330 (11') inflatable keel and Johnson 9.5hp Sportwin in the water this past weekend. The motor ran great and no leaks from the boat, so thats a huge relief.

I was a little disappointed in the speed though, as it took a long time to get on plane and top speed was only about 11-14mph. I had 2 guys weighing 180lbs a piece, 3 gallons of gas, and minimal gear.

I think the major issue was that the boat was porpoising quite a bit, with the prop audibly coming out of the water. So I've got to check and make sure I have the trim "down" all the way. But, should I consider a hydrofoil also? I was hoping for 15-20mph with a couple guys on board.

I had the dinghy inflated as much as my hand pump would go (good quality Coleman dual-action pump), and the motor was professionally tuned up, so I'm confident its running right.

 

[alanfox55]

It could be you could use a different prop but full inflation of the tubes and keel are also important. Get yourself a good air gauge so you know for sure what your pressure is.

 

[Sea Rider]

That's a air deck sib, as Alan recommends get yourself a nice pressure gauge, inflate all tubes to at least 3.0 PSI, keel to 3.5-4.0 PSI and air deck to 10-12 PSI, will need a electric or good hand pump to reach those numbers. With weight evenly distributed you should not trim engine down, as will lose best prop thrust. Buying a short shaft boat along a short shaft engine will not always match 100% of times. A 0.5-1.0 inch in tail height difference will make a nice boating day difference.

Try you solo driving, place a mate up bow, can sit at bow's air deck. Trim engine to be perpendicular to water level, usually 2-3 hole out transom, go for a wot spin and check if performance gets any better. A 9.5 HP engine is a poor performer with 3 up on a relative short sib, will need a induction tach along a prop maximization to get the best out of that engine to have fun. Installing an hidrofoil is useless if you are already experiencing prop aireation.

Had exactly same 330 model moons back, luckily ordered the wooden model, with an Evi 9.9 updated to 15 HP performed nicely with 2 up.

Happy Boating

 

[Guest]

i have a friend with a 62' rude and a friend with a 9.8 hatsu and the hatsu blows him away. same boat which is a 12ft azzuro mare. i am positive that outboard is not the main issue when it comes to planing its the psi in the floor. i had a friend put his airfloor in my boat and we could not plane. he refused to inflate the floor thinking its going to damage it. A wise man one said " inflate it until its rock hard and this will solve your problem". we must of answered a dozen questions already all leading to the same thing. THE AIR FLOOR IS A BICH

 

[fbpooler]

The old 9.5 motor does not have a thru hub exhaust and will not produce the speed of the 9.9 motors, but a prop change might be in order which may help with the speed. The information the guys are giving about pressures is right on also.

 

[Joe5.0]

Thanks guys, so what would be a reasonable speed at WOT to expect with 2 guys and 100% fully inflated?

I'll get a guage to make sure its inflated correctly for sure, as I guess its possible my pump isnt strong enough to get it drum tight. This is the hand pump I use to finish it off after the electric one starts slowing down.

 

[Joe5.0]

And I really dont want/need the 9.9 or 15hp versions, as from what I've read they weigh 75+lbs, which is more than I want to be taking on & off.

This one at 60ish lbs is heavy enough already, IMO.

I have a dinghy mate fuel tank, which bolts to the transom. So its not really logical to move it forward. :/

 

[Guest]

10-13 mph sound right with 2 up. It you do not get the weight distributed properly, you will not enjoy your boat. I would love for my tank to be right against my transom but weight does not allow it and wont let me plane. When i ride solo i need to push it as far up as possible. I still sometimes lean forward when i want to get on a quick plane. Plus i sit on the tube, one time i hit chop while siting on the bench and the bench came out and i almost fell out the boat. Now i only sit on the left tube.

 

[Joe5.0]

So I ordered a stingray jr. hydrofoil and I have an air pressure gauge that hopefully will work.

Before I install the hydrofoil I'm going to double check the trim and take it out by myself to see how it performs.

 

[Guest]

don't waste your money go cancel the order they are useless

 

[Chopperbill]

Had a Tohatsu 9.8 four stroke on my current boat a 5300 feet. It wouldn't do squat without the Sting ray Jr. However I learned a lot about inflation since then, but the Sting Ray still makes it plane faster and stay on plane at a lower speed. It might have an extra mph or two without it but it's staying on, even with my 20 hp Suzuki.

 

[Sea Rider]

If you learn under trial and error how to proper ballance weight evenly on deck, you don't need a doel fin. Besides if fin and sib does not ride parallel to water level while on plane, will experience fin drag that willl slow you down including increasing steering load.

That's with sibs/ribs being powered with max HP engines factory recommended. If slight underpowered a doel fin will do its homework as intended. If way underpowered, no way.

Happy Boating

 

[Chopperbill]

My 12' boat riding solo at sea level will look like it's going to flip over on take off unless I use a very long tiller extension and get as far forward as possible without the StingRay. It's damn scary when I'm in the back a couple of feet from the motor without the Stingray. Witnesses say it's looks like I'm going over. Will ad I weigh 220 lbs, lighter person my fair better. 20hp really is not underpowered as far as I'm concerned. Had some 25mph runs ridding two up with StingRay depending on river water conditions. I know some are against the StingRay, but I'm willing to give up a couple of mph for the comfort of sitting more towards the rear and not having to stretch back to a tiller. Riding two up we have to ride have to both bunch up in the middle for best full speed riding. Not why a went with a 12 footer. Also putting fuel tank and all the gear clear in the bow is not an option. Believe me I have tried every set up possible. I'm back at mile high altitude now so I'll probably swap out my 10 prop to my 8 prop to keep a faster and lower Speed plane. SIBs in my belief are just too light in the bow and heavy at the stern to get perfect all around performance. But, it's my best option for traveling without double towing, out side of those pricy foldable RIBs. Some think I'm crazy but it works for me, and I'm done messing with motor height, trim, and calulating sitting positions. Just going to enjoy what I got. Until I can slide a WinBoat by my wife. LOL
Ps. My boat was the fastest inflatable boat on the River this winter, most were envious.

 

[fbpooler]

A Sting Ray Jr. will definitely help some rigs even with the extra drag. I ran a 25 HP on a 14 ft fiberglass which lost a MPH or two but made the boat more stable and much easier to handle and got rid of porposing. A 15 HP on the same boat had no need for them. An inflatable club in the St. Pete area swore by the improvements they gained with their boats.

We installed a Doel Fin on an 85 HP pushing a 20 ft boat and also a 120 on the same boat and noticed improvements in both cases. Both motors had power trim and were infinitely adjustable while the boats were on plane.

We ran a 150 HP on a 21 ft boat which was a dog until we put Bennet trim Tabs on her.

The only way to find out what the effect will be on your rig is to try one. I read a series of tests many years ago which came to the conclusion that standard cavitation plates on motors were a compromise in many cases.

 

[Joe5.0]

Well I'm definitely going to try the Stingray Jr. as there's really no downside, and if its terrible I can return it.

I'm not looking to have a speed demon, I just want to be able to plane a bit easier and not need to be WOT all the time.

 

[Sea Rider]

Wot is used to plane faster provided that sib/rib is well ballanced and trimmed, once on plane can throtttle down to suit yout boating speeds and needs. Test a Stingray Jr. and check if works as intended,

Happy Boating

 

[Joe5.0]

Yeah, well I had to stay WOT to stay on plane, and the boat was porpoising so bad it was ventilating the prop. I'm hoping the hydrofoil and balancing the weight better solves the problem.

 

[fbpooler]

One thing to remember about the 9.5 as compared to the 9.9 is that the 9.5 is of an older design known for torque rather than flat out speed. It delivers its horsepower at up to 1,000 or 1500 RPM less than a 9.9 so has an entirely different power curve. It will be interesting to see the outcome of your test.

You are not going to outrun a 9.9 but should find your combination enjoyable. The 9.5 could be considered a fishing workhorse rather than a race horse.

 

[CapeAnn]

I have a 15 HP Tohatsu and I get up to plane and 20 mph easily with the wife and dog. Dog weighs 18 lbs. Having a couple of guys weighing combined 400 lbs is a fair amount of weight. Did the same 400 lbs + with a Tohatsu 9.8 and getting the same speed wasn't possible. That said - I was in Alaska in choppy conditions.

 

[Sea Rider]

+ 170 CC of the 15 made all the planing difference. Lightly loaded a 9.8 HP should plane that boat, if not, a prop maximization will do the trick.

Happy Boating