Top speed?

[summitlt]

I have a 74 Glastron V156 sportster with a 85hp merc inline 4. 15' 6" long by the way.

What do you think the top speed should be? With the right prop?

 

[Bondo]

Re: Top speed?

Ayuh,... 35/ 40mph...

 

[tashasdaddy]

Re: Top speed?

if v hull agree with 35-40, if tri hull cut it 5mph.

 

[summitlt]

Re: Top speed?

It is a Tri-hull. So tri hull is slower? Was thinking it would be inbetweena v and a flatbottom

 

[chiefalen]

Re: Top speed?

My 2 cents, to stay within the recommended rpm range, and the largest prop and with a gps you tell us.

For example, rpm say can't go over 5000 rpms, i don't know what your motors max rpms should be, this is a example, and a pitch on the prop say of 19.

That would give you the best top end.

Now as in everything with boats there is a compromise.

Want to pull skiers or tubers, the hole shot will suffer.

So you may want to go down 2 degrees for a better hole shot.

So the question you have to ask yourself what do i want to do with the boat?

Fish, get to the fishing hole faster?

Pull skiers ?

Now i always carry a spare prop for that very reason, a pitch propeller 2 degrees lower than the max rpms prop.

So when i go out in the morning to fish i get to the other side of the lake faster 9 miles away and of course in a hurry.

Then when it's time to put the poles away and the other kids want to ski i throw on the prop with the better hole shot.

Hope i was clear. And good luck.

 

[Frank Acampora]

Re: Top speed?

Glastrons before 1980 were a light, fast hull. V156 should be rated for a 90. Prop her correctly and with the Merc 85 she should go around 45 with 12 gallons fuel and driver. Be disappointed with less. Figure 36-40 with two passengers. Small boats respond negatively to extra weight. Still will be an excellent ski or wakeboard package though.

You may need to raise the engine about 1 inch on the transom to get full performance.

Want more info? Go to classicglastron.com

 

[QC]

Re: Top speed?

a pitch propeller 2 degrees lower

You meant two inches lower . . .

 

[chiefalen]

Re: Top speed?

^^^^^^^^^^^^^^^^ What he said^^^^^^^^^^^^^^^^^^^^^^^^

 

[45Auto]

Re: Top speed?

My 1980 Mark Twain trihull with a Merc 120 runs mid 30's with one person and 5 gallons of gas on board. Never seen over 35 MPH. But it also averages over 6 MPG which amazed me!

 

[BMWboatski]

Re: Top speed?

25-30 tops with that body style

 

[RotaryRacer]

Re: Top speed?

25-30 tops with that body style

Umm. I think it will be more than that.

I had a 15' '73 Saf-T-Mate tri-hull with a 70 HP Evinrude that did a little over 35 mph. That Glastron with an 85 HP Merc should go at least that fast, probably a little faster. I wouldn't be surprised at all if it did 40 mph.

The wetted surface of a tri-hull on plane isn't that much different than a V-bottom. They can be pretty quick. In the mid 70s they were building boats very light which helps also.

 

[summitlt]

Re: Top speed?

Best I got out of her was 37mph this summer, loaded. But the prop is dinged and I don't know the condition of the motor yet. Havent done a compression check or anything. Just seeing if I was in the right area.

 

[RotaryRacer]

Re: Top speed?

Best I got out of her was 37mph this summer, loaded. But the prop is dinged and I don't know the condition of the motor yet. Havent done a compression check or anything. Just seeing if I was in the right area.

Was that GPS speed? What RPMs was the motor running at that speed?

It really doesn't sound too far off from what would be expected for that combo.