glastron gt150

[evilrude 1]

I have been reading some posts about filling in a concave pad on the hydrostream viper/vectors and was wondering which would be faster and more controlable. Reason being I have just built a concave pad on a glastron gt150 that is 8ft long and 8 inches wide.
Right now its just glassed in and not finished and would have no problem filling it in if I wanted to.

Any imput would be great.

[evilrude 1]

Here is a picture to show what if done.

[vector mike]

I use to have one of those boats. Why would you want to put that concave on there? I would think that a flat pad would work better. I filled in my concave and removed the hook on my Vector contrary to what some people say and it handles great. The only difference I noticed was a little more wave slapping noise.

[evilrude 1]

I was thinking that the concave pad might pack some air under there and free-up the hull a little.
...So with your vector there was no difference in speed when you filled in the pad ?

Great boat you have there--- I've always loved those BP outboards

[vector mike]

Thanks. There are a lot of opinions about reshaping the bottom of the Vectors but I did it and it worked out great for me.

[gregpro50]

Those GT-150's handle aweful at speed and are pretty dangerous. I'd be interested to see if that modification makes a difference.

[rock]

I'm with Mike on this one. I filled, widened, and somewhat straightened my Vector and it ran and handled very well. I have heard all the arguements against it but it worked for me. I think your GT would benefit greatly. JMO

Rock

[evilrude 1]

I have heard (and been warned) by many that the gt150 is a hand full at speeds over 50 but for some reason I couldn't resist picking it up when I saw it.
But I do realize that for the higher speeds that I'm after I needed to do some serious work to the hull.
I plan on continuing the 1st strake all the way to the transom.
I have also cut out the splash well and will be glassing in a piece of plywood making a flat rear deck boxing it all together with external stringers. doing this will make the transom 26inches tall.




here are some pictures of my Thundercraft Playmate with external stringers that I built. NOTE: the width of the transom and floor, (the distance between the stringers)
I plan on doing the same to my gt150.

[gregpro50]

They chine walk really really bad around 55 or so. It is just plain uncontrollable and can get out of hand in a hurry. They were designed as a ski boat and not a go-fast boat. The other weak area in their design is the transom. They only have a partial transom that doesn't extend all the way to the sides so they flex bad. Those knees are definitely needed. I can't picture the concave pad doing anything more useful than a flat pad would do.

You'll definitely want to run solid motor mounts and make sure the rigging is good.

My GT-150 scared the hell out of me at 55 and now that I have a Hydrostream I can run 80+ mph in relative comfort.

I just bought another GT-150 as a project but I only intend to use it as a lake cruiser. I agree that they are one of the best looking boats ever made.

[evilrude 1]

I had a 16 foot picies (checkmate mx15 clone) with a 150xs on it and I know exactly what you mean about chine walking. That thing would "kill" over 50.

For this glastron I have a 81 johnson 140 . I am in the middle of rebuilding it with light weight forged pistons, full port job including finger ports, lightweight fly wheel etc-etc. I'm hoping for around 160+ hp. I am also going to use solid mounts and dual opposed ride guide steering and a 4" jack and of course a foot throttle.
I'm hoping to see at least 75+ MPH.

[gregpro50]

Well I guess all I can say is "may the force be with you".

That thing should be an animal with that motor. Mine had a Merc 115 and it felt WAY overpowered with that. Hopefully the mods you are making will calm it down a little.

I know mine was really light in the bow and even with the motor mounted to the transom and it still bounced pretty bad. I'm concerned that moving the motor back 4" will make it porpoise even worse. I think personally I would look for a jack plate with the least amount of setback. I didn't have a low water pickup on mine but I wonder how it would handle with the motor mounted really high and using a surfacing prop like a chopper or srx.

I'm really interested to see how you make out with this. I just can't imagine what 75mph would be like in one of these. I think the power you have planned would push it there if the boat lets you.

[vector mike]

My GT had the "Tower-of Power" 150 on it which is more like 120 at the prop and it was fun to drive. I definatley wouldn't want anymore HP than that on it.

[evilrude 1]

I've always likes over powered boats - I used to own a 13 ft Kennedy with a 140 Chrysler Charger motor running a cleaver prop (almost uncontrollable) but very fun.
and lately I just sold a hydrostream Ventura with a ccc evinrude Now that thing would almost barrel roll when you floored it and would still stand up straight at 40 mph when you stood on it.
But with my gt150 I guess I'll just take it easy at first and gradually try and go faster as I learn its temperament.
I will be using a stock l/u that I filled in the upper 3 cooling holes and hogged out the lower hole - to as low as I could, which is about a 1 inch rectangular hole and sculpted a path to the inlet opening from about center line on the bullet. As for props I have a 23p v4 srx, 24p worked sm. blade chopper and a 27p srx. One of these should get me to the speeds I'm looking for.
I'll post a picture tomorrow

[71V153]

All's I can say is you's a brave man ER. That hull in stock configuration was never designed to do anything over 50 or so. If you're not scared by then really scary things start happening around 55-57.

I agree the GT150 is one of the best looking boats ever built, and being a huge fan of old Glastrons I sincerely hope you succeed. But I ain't holding my breath. 'Course with major modifications who knows? Good luck!

[evilrude 1]

I appreciate the concerns of everyone who has replied and will put safety 1st and speed 2nd. But I do plan on rigging and setting this thing up properly. I also plan on taking my time to learn this things idiosyncrasies.

Here's some pictures of the work in progress.





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