Correct Prop?

[HawkeyDawg]

Hi there!

I just bought this little 11' hydro and I'm having a few problems with ventilation and performance. If I tilt the motor up to the point at which the attitude of the boat is correct, I have problems getting the boat on plane with 2 people in it, but when it finally gets on plane, it seems to work well.
With only 1 person (how it will be used mostly), the angle still seems to keep the nose up where it belongs, but I start having ventilation issues. When I tilt the motor down, it planes easier with the same load, but whether there is one or two people, the nose "plows" a bit and makes it a bit hard to handle at higher speeds.

I don't have power trim, and because of the design of the hull, I just about have to remove the motor in order to remove the tilt lock pin and change the motors tilt. Because of this issue, it's just not practical to switch the tilt angle all the time depending on load etc.

I have what I think is a Mercury 10x16 aluminum prop (the number on the prop is 48-73142 A40 16P). In reading about props and ventilation, it seems some props are designed to lift the bow, so that a lower tilt angle on the motor would work for my situation. Can anyone reccommend a prop that can get the boat up on plane with a heavy load, and not have ventilation issues? That way I could leave the tilt at an angle more suited to getting on plane with a load, and then the prop would lift the bow more than the prop I have now.. I realize I may have to sacrifice some top end speed for low end torque and I'm ok with that.

I forgot to mention the motor is a 35hp (1986) merc. I can't find the weight of the boat anywhere on the boat, but if someone knows how to find that sort of thing the boat was manufactured in Canada by F T Fibretech. The Model number is SS 3085. Hull number on the tag says 257956, and the number on the transom is Z FT 00275G585.

I'm just learning about props and hope I have given you all the info needed to help me make a good choice. The boat has no speedo, and the tach is not working yet, so I can't tell you any speed or rpm info

 

[jcsercsa]

Re: Correct Prop?

I'm not the expert here , I guys are going to tell you . you need the gps speed and the rpms . the rpms tell what the motor is doing so that is a major thing you need !! John

Ps sweet little ride !!

 

[cribber]

Re: Correct Prop?

If you can get a chance or already know, post your max WOT RPM, GPS speed, gearing ratio along with HP and pitch which you've provided. The experts here can help you fine tune the setup of your boat. Good luck!!! Weight wise I'd say you're in the 1500 lbs range fully loaded.

 

[steelespike]

Re: Correct Prop?

A cute little rig.Eventually you will want to lose the foil.It will be a little harder to plane and may bounce a little but should improve your speed
You can allways add smart tabs if bow bounce is a problem.
Your venting indicates your motor most likely is right at its max height
for best performance.You might consider a 3 gallon tank The motor should run more than an hour at wot(wide open throttle) on 3 gallons.Also for your use a little Garden treactor battery will save some weight at the stern.
That rig will pretty much allways be slow to plane.The old time race boats used to have the same problem driver usually had to get up and lean on the bow.Not really prectical in every day operation.Check out the Turning point Rascal (I think available for your motor)It should solve you venting issue and most likely improve performance across the board.Close to stainless performance at aluminum prices.But before changing props get a tiny tach and a gps and get your max rpm and speed.On the tinytach get wire long enough to mount in front of you you can't add to the wire.Simple installation and reasonable price.
The 35 is rated for 5,400 to 6,000 rpm.You need to prop for above 5,400
for best performance.

 

[Frank Acampora]

Re: Correct Prop?

See my tunnel hull in the avatar? These little boats are so stern heavy and so overpowered that the only way to get them on plane without power trim is to lean over the steering wheel. Nail the throttle, lean over the wheel, and as she breaks over into plane be ready for, and react to, a strong pull to one side. Be careful! Most of these little boats are unforgiving of driver error and a bit unstable at speed.

IF you are experiencing ventilation at the correct engine tilt you have basically two options: 1 Lower the engine a bit on the transom--not desirable 2. CUP the prop.

Try asking about your boat on Hydroracer.com.

And BTW: even though the capacity plate may state two people, that boat will really only be comfortable for one. And, you really should consider moving the gas tank and battery up under the bow.

If you want to see a better photo of my Cub, send your email address to me in a private message.

With the Merc 35, speed will range anywhere from 30-45 MPH depending upon your set-up , hull, and load. They don't really go too fast, but because of their size they feel like they are doing 100 and they are a classy, fun ride.

Mine is a 10 foot Cougar Cub. I am running a Chrysler 50 with a 10 X 16 fully cupped two blade racing prop. I have the battery and tank up under the bow and still need to lean over the wheel to break her over. However, the higher the horsepower, the faster she will drop onto plane.

Your 16 pitch prop is probably correct. You have a very light load. The whole rig probably only weighs a bit less than 700 with one person in it and you need pitch to get the top speed

 

[HawkeyDawg]

Re: Correct Prop?

Thanks for all the input guys.

I will try to get the gps speed and rpms.

The installed tach is an old Airguide... I love the look of it and am wondering if anyone rebuilds those old dogs? If not, what kind of tach do I look for? I'm also not real knowledgeable about tachs.... are they built specifically for a certain number of cylinders, or does that make a difference? Can an automotive tach be used if silicone is used to make it water resistant?

Thanks again to everyone for the help. It's hard to know which people to trust when looking locally for help. Seems most shops aren't as interested in solving these kinds of problems as they are in how much money you can spend.

Go Hawks! and congrats to Windsor...

HawkeyDawg

 

[steelespike]

Re: Correct Prop?

The tiny tach (about $40)uses plug wire pulses with a special wire wrapped around a plug wire.My 5 year old grandson could do the basic hookup with my guidance. Tach for your motor will work on any 2 cylinder 2 stroke.
I believe you could use it hand held in a temporary install. Contact tinytach for details read and understand their info.
I'm sure there are other tachs but most probably cost more and require more complicated hookup. I believe there are some on here that have put TT on motors as small as 6 and 9.9 hp.