Help me get the most speed out of my boat

[sticky30]

Ok heres the deal, I have a 1436 jon boat with a '97 mercury 20hp. I had a alum 13" prop that was eaten up pretty well from the previous owner hitting stumps. So I bought a pirraha prop, D hub 10 spline with a 10 3/8" x 15", now the boat does real well about 30mph with 2 people.

I want to go faster. I have not found anyone who makes a 17" or 19" pitch prop to fit my motor. I know there is good reason for that and going any faster would be insane in a boat that size. But still there must be a way to get a bigger pitch prop for my motor.

Is it possible to find a prop say 10x17 or 10x19 and install a hub kit that fits my prop shaft (10 spline)?

Please give me some helpful suggestions. I know it unsafe to go faster in that boat but....
Thx in advance.

Spencer

 

[dieselcat]

Re: Help me get the most speed out of my boat

If you can't find it they probibly don't make it.If not your only other option would be to buy either a aluminum or stainless prop and take it to someone in your area that works on propellars and have it re-pitched.I know you can have a stainless prop re-worked not sure bout aluminum.good luck hope this helps!

 

[Sandhammaren05]

Re: Help me get the most speed out of my boat

If you want to go faster first thing is get the cavitation plate above the boat bottom. Is your prop cupped? If not, it must be in order to run the motor higher than 17" or so on the transom. Check with Ron Hill for props

http://stores.shop.ebay.com/Ron-Hill-Propellers__W0QQ_armrsZ1

You can't necessarily swing more pitch. The motor should be turning around 6000RPM, much less than that and you're just bogging the motor. Get a tach if you're serious. Do you know the gear ratio of the motor? Check out Stilleto props too. How did you measure 30 mph? I don't understand your boat length below. A small boat is not necessarily limited to low speeds, depends on how well the boat handles. I've run 80 hp on a 13' boat, 30 hp on an 11' boat, etc.

Ok heres the deal, I have a 1436 jon boat with a '97 mercury 20hp. I had a alum 13" prop that was eaten up pretty well from the previous owner hitting stumps. So I bought a pirraha prop, D hub 10 spline with a 10 3/8" x 15", now the boat does real well about 30mph with 2 people.

I want to go faster. I have not found anyone who makes a 17" or 19" pitch prop to fit my motor. I know there is good reason for that and going any faster would be insane in a boat that size. But still there must be a way to get a bigger pitch prop for my motor.

Is it possible to find a prop say 10x17 or 10x19 and install a hub kit that fits my prop shaft (10 spline)?

Please give me some helpful suggestions. I know it unsafe to go faster in that boat but....
Thx in advance.

Spencer

 

[steelespike]

Re: Help me get the most speed out of my boat

If your serious about speed get yourself a gps,and a tinytach(reasonable,easy install) I believe your rpm range is 4,500-5,500.You should shoot for a prop that developes close to the max.Its bad for the motor to operate at wot(wide open throttle) too close to the bottom end (lugging)or beyond the top end.(over reving)Do a test to see how it actually does.
let us know what you find.It appears the Pirahna can perform very well
and is an excellen candidate for experimentation.
The turning point Rascal is an aluminum that delivers stainless performance at aluminum prices.

 

[sticky30]

Re: Help me get the most speed out of my boat

Ok, looks like i might need to try and raise the motor. But did i read that right, the prop has to be cupped before the cav. plate can be raise above the hull? I'm not sure if raising is gonna make a difference with top end in this case because i feel i cant get anymore speed out of that 15" prop. I mean at some point it wont go any faster, right? Unless i figure out how to get more rpms. Maybe that is the way i should be heading.

More info on motor/boat 14' jon boat so the handling is poor in the turns at higher speeds. Motor wot 4500-5500, speed was measured with gps

 

[steelespike]

Re: Help me get the most speed out of my boat

The idea of raising the motor is to drag as little as possible through the water.
Under ideal conditions a 2" increase in height could net close to 2 mph.
I think your composite prop may work.If not the Turning point Rascal will.
It is still critical that you get a tach.Speed without the rpm really tells nothing.30 with 2 aboard is a pretty good figure.

 

[Sandhammaren05]

Re: Help me get the most speed out of my boat

If you raise the motor and an uncupped prop doesn't cavitate ("ventilate") while planning off then the motor's still too deep. Getting more gearcase out of the water decreases the drag, which increases the speed, but the prop must be cupped. GPS is good. Wear a kill switch, especially if you're using a tiller handle! A boat that 'feels' too fast IS too fast for you, whether it's at 90 mph or 20 mph. You need to pay attention to water conditions and traffic and stay under complete control of the boat at all times. A jon boat is not going to turn like a V-bottom, so don't expect it to. When I drove raceboats at 85 mph they never 'felt' fast under traffic, water and wind conditions, even with 50 boats on a 3.5 mile course. I nearly blew over a 14' bass boat with a 15 hp motor at 20 mph last Nov. because the wind and waves were so strong (came off a big wave, climbed out of the water bow high and came down sideways), so be aware!

Ok, looks like i might need to try and raise the motor. But did i read that right, the prop has to be cupped before the cav. plate can be raise above the hull? I'm not sure if raising is gonna make a difference with top end in this case because i feel i cant get anymore speed out of that 15" prop. I mean at some point it wont go any faster, right? Unless i figure out how to get more rpms. Maybe that is the way i should be heading.

More info on motor/boat 14' jon boat so the handling is poor in the turns at higher speeds. Motor wot 4500-5500, speed was measured with gps

 

[steelespike]

Re: Help me get the most speed out of my boat

That reminds me of a story told here some time ago.
small jon boat with too big a motor somehow threw the driver out on a fall day ,no one around.Boat continued on and beached.Two guys who saw it happen used the beached boat to rescue him.He is convinced without that stroke of luck he wouldn't be around to tell the story.

 

[Sandhammaren05]

Re: Help me get the most speed out of my boat

Always wear a kill switch. Kill switches were required in NOA after the 1958 nationals, when clamp brackets broke on 2 Scott 40s throwing the drivers into the water. One was run over as the boat circled. It's not only for jon boats, every driver should use a kill switch.

That reminds me of a story told here some time ago.
small jon boat with too big a motor somehow threw the driver out on a fall day ,no one around.Boat continued on and beached.Two guys who saw it happen used the beached boat to rescue him.He is convinced without that stroke of luck he wouldn't be around to tell the story.