Need help with slow Glastron

[kickin79gp]

Hi all, I recently bought a 1971 Glastron V143 with an early 80's 70hp Merc on it. So far the best speed I've reached with it was 35mph with a 12P prop and about 32 with a 14P. I do not have power trim and tilt or a jack plate. No matter what I've done so far, like tilting the motor up I just can't get any more speed. I would really like to make this boat reach 45-50mph so I can do more than pass pontoons and small fishing boats. I need some advice on what type of mods I can or can't make with this boat. I have no idea what this boat can handle. The hull, floor and transom are solid. After the amount of wave pounding this poor boat gets on Lake Wisconsin, I swear it's bullet proof. Anyway, I'm wondering what I can do to get this boat moving. Are there any secrets to this boat? Is there any possibility of building this type of engine? Any suggestions on motor height, set back, or anything else that could help me would be greatly appreciated. :confused:

[AlaskaStreamin]

There's not much you can do to your motor. You would be better off selling the 70 and getting a 90 with power trim and a stainless prop.

[Rickracer]

....you'd be much better off with an OMC V-4. Way more power stock, and highly modifiable. A better bet would be to just keep the thing together and enjoy it till you can afford a more performance oriented hull. :cool:

[glassing oldie]

Hi all, I recently bought a 1971 Glastron V143 with an early 80's 70hp Merc on it. So far the best speed I've reached with it was 35mph with a 12P prop and about 32 with a 14P. I do not have power trim and tilt or a jack plate. No matter what I've done so far, like tilting the motor up I just can't get any more speed. I would really like to make this boat reach 45-50mph so I can do more than pass pontoons and small fishing boats. I need some advice on what type of mods I can or can't make with this boat. I have no idea what this boat can handle. The hull, floor and transom are solid. After the amount of wave pounding this poor boat gets on Lake Wisconsin, I swear it's bullet proof. Anyway, I'm wondering what I can do to get this boat moving. Are there any secrets to this boat? Is there any possibility of building this type of engine? Any suggestions on motor height, set back, or anything else that could help me would be greatly appreciated. :confused:

Hi - just a thought but has anyone considered the weight of the boat all up ? Older boat have a lot of wood built into there construction and glassed over ,usually never sealed completely when it was put in from new . Because you probably use the boat in fresh water it naturely sits deeper in the water . It the wood in the boat will be soggy and wet and you could be carry around a extra couple of passengers all the time . Not only wood in the hull (transom , floor boards , seat frames. Side panels covered with upholstery and all those sorts of things ) but also Core and plywood pads in the deck .
With fittings screwed on to the deck surface and the way they were fixed the sealer will have perished and water gets in between the layers of core and plywood regardless of what it is and there could be another passenger going for a free ride .
The old motor will be getting a bit tired but have you checked the height it is set up at ? . The bottom of the cavitation plate should be a 1/4 inch below the bottom of the level of the hull . This could go up a bit higher but its a good starting point . Most motors are set a way to low and this does not do anything for the performance or the handling .
Cheers !

[AlaskaStreamin]

{QUOTE} The bottom of the cavitation plate should be a 1/4 inch below the bottom of the level of the hull . This could go up a bit higher but its a good starting point . Most motors are set a way to low and this does not do anything for the performance or the handling .
Cheers !

Sorry but I have to disagree here. The cavitation plate should never be below the bottom of the hull. You can go slightly higher but the stock prop needs to be buried to lift the bow.
I agree with Rickracer, a V4 OMC would be nicer than a 3 or 4 cyl merc 90. They weren't the most reliable motors.

[daytrader]

Years ago I had a 14 or 15 ft lite glastron hull (think it was a V1-- something or other. It had cable steering and a 75 50 hp johnson, I remember jacking the motor up slightly and it went pretty good for what it was, lot of fun, good luck with yours, Gary

[THE FAST ONE]

Hi all, I recently bought a 1971 Glastron V143 with an early 80's 70hp Merc on it. So far the best speed I've reached with it was 35mph with a 12P prop and about 32 with a 14P. I do not have power trim and tilt or a jack plate. No matter what I've done so far, like tilting the motor up I just can't get any more speed. I would really like to make this boat reach 45-50mph so I can do more than pass pontoons and small fishing boats. I need some advice on what type of mods I can or can't make with this boat. I have no idea what this boat can handle. The hull, floor and transom are solid. After the amount of wave pounding this poor boat gets on Lake Wisconsin, I swear it's bullet proof. Anyway, I'm wondering what I can do to get this boat moving. Are there any secrets to this boat? Is there any possibility of building this type of engine? Any suggestions on motor height, set back, or anything else that could help me would be greatly appreciated. :confused: HAD ONE OF THOSE AT ONE TIME,RAN INLINE 140 & 150 ON IT.2-BLADE BRONZE PROP LOTS OF CUP,RAN PRETTY GOOD.GET YOURSELF 9O 0R 100 ABOUT 22P SMALL HUB LAZER-2,SHOULD SATISFY YOUR NEED FOR SPEED,LOVED THAT BOAT,SKING,PLEASURE RIDING,A LITTLE HOT-RODDING--ED

[jeffbare]

There is always the option of putting a pad on the bottom. Look for Alaskastramin's thread about putting one on a bayliner.

[GT-150]

:D Hi: A 90 Merc Will not do it. It won't do it on my GT-150, 42 is max with a regular 21 pitch at 4800RPM, Trimed Chiming fairly good got near 44. 19 Pitch does about 38 at 5000 and 39.5 at 5200. A 115 Merc 6 may give you an extra 2/3 MPH turning a 21 pitch, one simular to mine with 115 Merc does 45/6. You'll need a 140-150 to get into the 50s. I Like My Mercs but a 150 is Heavy, go with a 140 Johnson which weighs about 8-10 pounds more than my 90 merc.Late 70/s Earely80s Johnson 140 Horse(Small Block) weighs 308 pounds. That's what my choice would be for my GT-150. Your 70 Merc should weigh around 190 pounds. So would suggest Transom Strengthing but may be simpler and cheaper to look for a Quicker ride.:cool:

[Tampa Cat]

My 16ft glasstron had a v4 115hp.I think it ran 45 mph or so with a steel prop on the omc speedometer.It was a good fun boat but I wouldn't of liked it at 35 mph.

[THE FAST ONE]

My 16ft glasstron had a v4 115hp.I think it ran 45 mph or so with a steel prop on the omc speedometer.It was a good fun boat but I wouldn't of liked it at 35 mph. THIS BOAT IS 14'3" THAT IS WHY IT IS A 143 GLASTRON.

[brettster98]

im running the 20' 3" glastron ski machine with a 225 efi merc 3.0 liter on the back boat runs around 65 with a 4 blade 27 pitch small hub. the boat use to porpoise with out the windshield on handles way better with it.

[glassing oldie]

im running the 20' 3" glastron ski machine with a 225 efi merc 3.0 liter on the back boat runs around 65 with a 4 blade 27 pitch small hub. the boat use to porpoise with out the windshield on handles way better with it.


Interesting , the windsreen has made the differance in the handling ? Do you know why ?????

[brettster98]

ya with gas tank in the front & with a full tank 26 gallons the boat would handle decent but by half to empty boat would get scarey..acts like a spoiler.we wre think that before the windshield was put on.

[glassing oldie]

ya with gas tank in the front & with a full tank 26 gallons the boat would handle decent but by half to empty boat would get scarey..acts like a spoiler.we wre think that before the windshield was put on.

You are approaching the danger zone of where Hydro dynamics leave off and aero dynamic take over and come into play .
This happens in speeds around 45 to 65 mph .
Was never a problem ages ago as we thought we were flying at 45mph .
As speeds have increased with bigger motors and lighter boats thinking has not moved with the times .
This is what makes tunnel boats perform , riding on a cushion of air under the hull in ground or surface effect and getting lift from the deck and top surfaces just like a wing on a aircraft.
By putting the screen back on you have changed the airflow and the aerodynomics .
Shfiting weight is not solving the problem of being aerodynamicly unstable .
Going into the wind couldget a bit hairy ,going with it not so , depending how fast the wind is blowing of course .
Any one out there got a tunnel boat ?
Check the shapes they have on the decks etc , they are made to fly !
Check out aeromarine and see the articals they have on this very subject .
Got good life insurance for the family have you ?