14hp + mc366

[fbpooler]

12 ft x 80 in is an extremely wide boat and would depend on weight placement more than a more narrow boat. Normally boats are about three times longer than the beam for a 1:3 ratio. I wonder now if it is not a hull design problem to start with and the squirrely reaction when accelerating is just normal for this design. Steering would be critical with such a wide beam.

If it is rated for 9.9 HP, the 15 should run the heck out of it. 15 MPH with the hull design might be good speed for the beast. We might be chasing shadows here and the problem is hull shape instead of a motor problem.

Imagine pushing a log up the river. If you push from the end you could control it. If you push from the side of the log, it would want to change direction on you.

Has anyone else run one of these hulls?

 

[Sea Rider]

Have seen some with speed tubes and without them,, are wider than any standard sib, that's why rated for higher HP engines, some even require L sizes to work well. So, the cat we're talking about needs a 9.9 or larger HP ? 9.9 is too basic performer with more than 1 up, minimum ideal would be a 15 or even a 20 HP, to take + 2 up and have more speed fun.

Happy Boating

 

[mrdrh99]

I'll be on the icw tomorrow guys.... I'll have more room to run it but my dad will be on with me.... May be interesting to see if we can get the weight right and get it on a plane

 

[fbpooler]

Read about that hull on the Boats to Go website which was a good read. Put a higher HP motor on that boat if you like, but make sure all insurance is paid up. It is designed for low horsepower and should do a beautiful flip when the bow blows back over the transom at speed. It is a scow type design, not a fast cat design by any means. Be forewarned.

Chopperbill is right on the money.

 

[mrdrh99]

Are you saying that the 14hp and running 16mph is dangerous in my boat?

 

[cablebandit]

add a Doel Fin to that motor and it will plane a LOT faster

 

[fbpooler]

There is a good chance that you could run into serious problems pushing that hull beyond design. You could rip the transom off the hull, as it is not supported against forward thrust with floor boards and only the ends of a wide transom are attached to the hull to prevent twisting of the transom. The shape is not aerodynamic, if that is the right word, and would tend to trap air which would provide too much bow lift at speed. As I have already pointed out, the ratio of length to beam is out of whack and there is little to prevent the bow from becoming airborne.

Just imagine that you are running at speed and hit a boat wake. The additional lifting of the bow could be severe. Also you noted that it was squirrely while accelerating.which was caused by forces effectively shifting under acceleration. That is why I used the example of pushing a log through the water from the side rather than the end.

This is not saying that it is not capable of providing many hours of enjoyment, and if used for what it was designed to do, it will. If pushed beyond design, all bets are off.

I one planed a canoe and it really moved. It was far away from what the craft was designed to do and in dangerous territory even though it planed. The long hull with insufficient beam would have rolled with me if I just moved chewing gum from one side of my mouth to the other. They instability as it gained speed was a warning I did not have enough sense to note before performing the maneuver. Coming off plane was an intense activity which could have flipped me suddenly.

After discussing the motor, I researched the boat on the manufacturers website. They make no bones about what it was designed to do, and running at high speed was not referenced. Referring to planing the hull with an electric motor caught my eye, as they were pretty generous with the description of planing. Perhaps they should have said skimming.

How that hull ended up having the data plate which is affixed to the transom is a mystery. They state 9.9 HP max right on the website, so that raises a large caution flag in my mind.

Go ahead and do your water test, but be watchful of any signs of problems while doing the runs. With experience you will learn to handle the craft right up to the point that caution is required, and a larger, heavier motor would not be a consideration as far as I am concerned. Things tend to break when the get a larger hammer thinking is followed. Down here in Georgia that is pretty much covered by "hold my beer and watch this".

 

[mrdrh99]

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FB.....14 is it.... No more. Went out on the icw today with my dad. It pushed us along nice and smooth at 9mph asking with about 100lb of gear. She handled wake from the big boys very very nicely.... At no point did we feel unsafe! Anyhow.... It was low tide so after using the cast net for bait we beached on a couple of sandbars and fished from there..... Very nice relaxing day

 

[Sea Rider]

Why don't you post some nice pics of the whole combo, transom, side views, bow to check that sib. Just curious about that model.

Happy Boating

 

[mrdrh99]

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Boat before launch

 

[mrdrh99]

Oh yeah.... One other thing about the way this boat "planes" ..... Once the weight is right it actual suctions down to the water.... Bow doesn't ride high at all and then the speed doubles. Not like others I've been in which seam to rise out of the water. It was strange because I was expecting the floor to be completely off the water and moving up on the tubes only

 

[fbpooler]

This is good to hear, and it was good you and your Dad had a special day together.

You can cover a lot of water at 9 miles an hour, and as it handles the wakes in the Intracoastal well, you have a dependable and enjoyable rig. Looks as if it swallows fishing equipment without cutting the space for the boaters also with the wide beam.

 

[mrdrh99]

Would there be anything to gain from hydrofoils? Maybe planning quick and easy..... Better fuel econ?

 

[mrdrh99]

Why don't you post some nice pics of the whole combo, transom, side views, bow to check that sib. Just curious about that model. Happy Boating

Just saw this.... I really need to clean it up so early next week I'll get it out in the yard and I'll get you some nice pics and a walk thru video.... I'm going to set it up and play with my seating and storage layout.

 

[mrdrh99]

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[fbpooler]

I think you would be happier with a normal inflatable which is designed to plane if you are looking for more speed. You are evidently running in displacement mode right now which protects you from having the bow lifted and possibly getting into dangerous territory. You effectively have an 80 inch wide wing under the front of that boat which is affected by air pressure at speed. In all probability that hull would run nearly as fast with a 9.9 HP motor.

A displacement type hull reaches design speed and any power applied after that point adds very little to the speed while burning more fuel. Getting 9 MPH with a 14 HP motor at full throttle is a fuel hog with much prop slip. Adding something which caused more drag to the lower unit would only retard the rig.

A hydrofoil adds lift to the stern so to find the difference, you would just have to try one.

In short, you are up against boat design in your quest for more speed, and how it would handle if running faster is the big question. It would not hurt to ask the manufacturer the questions you have posed here.

We have tried to answer your motor questions based on conventional inflatable design. Taching and propping the engine would insure that it is performing properly, but speed will be contingent on the hull design. That is a big question mark in my mind.

 

[JohnnyRudeClassics]

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Hear is a short video from this morning http://youtu.be/fPAXkTFWrbg

Looping the headphone audio output back into the microphone input
with a 1/8" stereo patch cord I had laying around and using
Soundcard Scope for the spectrum analysis, your motor's fundamental
audio frequency was 130.32 Hz.



For a 2 cylinder 2-stroke there are 2 combustion events per revolution,
so your motor was turning at 130.32 Hz / 2 = 65.16 Hz
multiplying by 60 will give you the RPMs
3909.6 RPMs ( +/- 27.15 Hz )

That sounds a little bit on the low side, I think I may have missed
exactly what motor you have when I skimmed through this thread, but
it sounds like it is an older ( > 30 years ) OMC and generally those
motors are rated to run between 4000 and 5000 RPM's.

If you are running under 4000 RPMs, you are lugging / over loading
the motor and should consider a prop with less pitch (it's like
shifting into a lower gear).

If you are running above 5000 RPMs, you are over speeding
the motor and should consider a prop with more pitch (it's like
shifting into a higher gear).

 

[mrdrh99]

Does adjusting the idle have anything to do with this?

 

[JohnnyRudeClassics]

idle adjustment is more for how slowly the motor will troll, not optimum high speed

 

[JohnnyRudeClassics]

I see it is now almost useless to post photos,
when I clicked on the one I included above,
it is barely a thumbnail....