Glastron GT160 , 115hp Inline Merc

[AMD Rules]

Hey folks, I don't think I've ever posted in the prop section....so here goes.

I've been toying around with a few props this past week, and I'm curious if someone may have valuable advice as to best route to take to squeeze a bit more speed out of this 'ol school vee hull.

Some data:

I was solo, so my rpm/speed data is limited. Water was a bit too smooth for optimum test. Gentle crests.

1972 Glastron GT160
1984 115hp Merc
Solo with 8 gallons fuel in the bow and 6 gallons portable fuel in reserve under splashwell

21P Bronze: 5600rpm max, 48 mph
23P Bronze: 5200rpm max, 47 mph
21P Ballistic: 5800rpm max, 53 mph
19P Aluminum: Not tested

I reached my goal of 50+ mph. I am quite happy with the stainless prop. Did not experience blowout in turns and was able to achieve significant bowrise for the first time ever. Finally experienced issues with chinewalk type of movement, which is likely a result of freeplay in the steering mechanism. Next steps is to improve steering, adjust trim tab to lessen strong side to side pull, and probably raise the motor vertically an inch or so.

The 21P bronze prop did not perform as expected. Appears it still has hub issues after rebuild. Disappointing.

The 23P bronze is too much prop for this setup as it is. 5200rpm is below required rpm at wot. Will hold onto the prop for now, as it may improve once the motor is raised. We'll see.

Ballistic is a champion. Couldn't be happier with its performance. I don't need to go any faster, but I'd like to try.

I wish I had some way to interface rpm, and gps speed into a laptop. For now, I made a curve by hand just to show the curves with limited data points.

GPS screenshot shows the 53mph speed obtained.

The questions:

Anyone familiar with these hulls, and feel that a 5" manual jackplate would be a good addition to help squeeze out a few MPH? Is it a waste of time with this hull? I'm considering a manual jackplate but not sure if thats a good idea or not. Lots of extra stress on my transom, and I've no pad at all to sit on. Advice online seems to be all over the place. Only real reason I'm leaning in favor is because I need a new steering system anyways, and in order to use the transom bracket steering I need to get my motor back away from the hull to fit the steering arm. Right now I use the original splashwell mounted steering arm (which I hate) which is all that fits. I'm not really familiar with how to hook up dual cable no feedback system ... but thats my goal I suppose. If I'm gonna do it, I might as well do it right. Knowing my luck I'll get it rigged up, hammer the throttle and the entire transom will snap off and I'll sink.

The 21P Ballistic is spinning a bit above the 5500 maximum rpm allowable for this motor. I'm thinking about trying to find a 23P, but it sounds like a lot of prop for this motor. Hull is said to be 800lb dry, plus motor, fuel, contents etc... I'm thinking its around 1500 to 1600 lbs in running mode.

Would greatly appreciate any thoughts, ideas, suggestions.

Thanks!

 

[AMD Rules]

Re: Glastron GT160 , 115hp Inline Merc

I should add that the jackplate I'm considering purchasing is a Bobs Machine MJ-5. Any thoughts on this particular model?

 

[Frank Acampora]

Re: Glastron GT160 , 115hp Inline Merc

53 is not too shabby! But, you still have a little way to go. Over at the Classic Glastron site there is a guy with a V153 (closed bow 4 seat pleasure hull) who is turning 55 mph GPS with a Merc Tower of Power 115. He also experiences chinewalk at those speeds.

I have a 14 foot flat bottom with a 125 on it. I have had it up to 55 with no ill effects. Once I get the engine running correctly I hope to get 60-62 MPH. Then I am going to experiment with jackplates and some bottom modifications, hopefully to get more lift and higher speeds. I also found that although a Force, the engine seems to like the 21 pitch cupped racing prop the best. I have had on 23 and 25 but they load it down and top speed suffers. It seems to want to run at about 5800-6000. Boat also gets a little squirrely. I have an absolutely BEAUTIFUL solid hub, 12 inch bronze, Merc racing 2 blade, which the engine can not swing--just too much pitch and cup.

Try the Glastron site. You will learn that your GT150 was powered with an Evinrude 130 and made the longest ever recorded jump --160 feet, in the James Bond movie "Live and Let Die" and a whole bunch of other interesting stuff.

Chinewalk is usually a function of deep vee riding height. The hull rises so high in the water at some speed that there is not enough area to support it and it falls to one side. This then makes it bouyant again and it rises and falls to the other side. It is kind of like a feedback loop. Better steering system may not help. Some chine rails to direct (the water that squirts straight out sideways near the stern) downward may help stability a bit and may also give a little extra lift for less hull wetted area and higher speed.

Notice my Glastron V153 in the avatar? It goes 42-45 with a 90 and a 19 pitched prop. Someday it will get a 140 that I have just sitting around.

 

[AMD Rules]

Re: Glastron GT160 , 115hp Inline Merc

Hi Frank,

Thanks for the comments. I'm an active member on the Glastron forum already. In fact, one of the props I have was sourced through the gentleman whose running the V153. My boat is a GT160, a little bit bigger than that boat used in the infamous bond jump.

I've not investigated chine rails. Will read up a bit to see if they may add any positive effects to this ride.

Sounds like you have a nice collection of hulls. Must be fun.

 

[Dhadley]

Re: Glastron GT160 , 115hp Inline Merc

"Back in the day" we sold Glastrons and the GTs were a lot of fun. I had a GT150 that we straightened the bottom on and it made a world of difference. It would have been great to have had jackplates then and I think it would have helped. The Bob's 4-n-1 is always my first choice in a manual because of all the adjustability. I really don't think you could go wrong. If I were doing it I'd consider taking a little hook out of the V (or U) out to the first lifting strake. However, if you're skiing it'll be better with it there.

 

[Turbo1]

Re: Glastron GT160 , 115hp Inline Merc

Bob's 4-n-1 is a super plate....likely you'll have to put the 2-blds on the shelf though...don't think they'll run as high as you'll be going.
I don't quite know what to classify that Ballistic in... some hulls it's faster, some not so fast. When you get the engine up the bullistic won't hook-up well-it WILL vent. I have 5-6 of those around as paper weights.
Too bad there isn't a TXP for that size of gearcase, aey DH?

 

[AMD Rules]

Re: Glastron GT160 , 115hp Inline Merc

"Back in the day" we sold Glastrons and the GTs were a lot of fun. I had a GT150 that we straightened the bottom on and it made a world of difference. It would have been great to have had jackplates then and I think it would have helped. The Bob's 4-n-1 is always my first choice in a manual because of all the adjustability. I really don't think you could go wrong. If I were doing it I'd consider taking a little hook out of the V (or U) out to the first lifting strake. However, if you're skiing it'll be better with it there.

Hey Dhadley... thanks for the comments. I'm not entirely sure what you mean when you say 'take a little hook out of the vee". I've seen a couple of boats where they flattened out the bottom vee (long pads), some shorter than others. Some widened the first lifting strake as well. Pic attached is a sidewinder, but would have had a similar profile to my hull originally. I will be tearig into this hull eventually for a floor/transom overhaul, so I'm not against talking about 'possible' modifications, even if they're just wild ideas. I don't want to make a hull thats set up completley for straight line hammer down but wouldn't necessary object to a compromise in general performance to gain some speed.

I'm in complete understanding that I'm dealing with 40yr old hull & motor technology, and its a pipe dream to expect too much from it. Let's assume I stick with a Merc Inline... what direction would you head if you owned this hull?

 

[AMD Rules]

Re: Glastron GT160 , 115hp Inline Merc

Bob's 4-n-1 is a super plate....likely you'll have to put the 2-blds on the shelf though...don't think they'll run as high as you'll be going.
I don't quite know what to classify that Ballistic in... some hulls it's faster, some not so fast. When you get the engine up the bullistic won't hook-up well-it WILL vent. I have 5-6 of those around as paper weights.
Too bad there isn't a TXP for that size of gearcase, aey DH?

No worries about the 2-blades. I have an older Merc 1150 they can be used with. I'm hoping I won't need to raise it too far yet, else I'll be looking for a low water pickup etc. Seems like a shame to go that far with only 115hp. If your 'van is parked close to a river' near me, I'm looking for a 23P <hint>

Been suggested that I should also consider a Merc Lightspeed 22P... any thoughts on that prop ?

 

[Dhadley]

Re: Glastron GT160 , 115hp Inline Merc

T1, I know where there are some 23" - 25" 4 blades made for an OMC V4. Not quite a TXP but I'll bet they'd run good on an old hull.

AMD, I did the same thing to a Sidewinder. I started at the V with a 4 to 6' straightedge. You'll find the hull dips right at the transom end. Probably a 1/4" or so. We took the hook completely out from the V out to the first strake. From the second one out we took out about 1/2 the hook. A real messy and time consuming pain in the drain but it sure makes a difference. I actually thought about adding a pad on the Sidewinder but didn't. I did have a manual Bob's on the 'Winder. Nice set up. Not an Allison but nice.

 

[AMD Rules]

Re: Glastron GT160 , 115hp Inline Merc

AMD, I did the same thing to a Sidewinder. I started at the V with a 4 to 6' straightedge. You'll find the hull dips right at the transom end. Probably a 1/4" or so. We took the hook completely out from the V out to the first strake. From the second one out we took out about 1/2 the hook. A real messy and time consuming pain in the drain but it sure makes a difference. I actually thought about adding a pad on the Sidewinder but didn't. I did have a manual Bob's on the 'Winder. Nice set up. Not an Allison but nice.

Thanks Dhadley, I didn't realize these hulls had an intentional hook in the desgn. What is a realistic height I can run on this 5" plate (which I have now) without a LWP? Should I be seeking a different prop to run above stock height?

Also curious about what steering you recommend, that would work with my older Merc. Will one that was intended for a V6 work with my setup?

 

[Dhadley]

Re: Glastron GT160 , 115hp Inline Merc

Almost all hulls have hook unless they're a high performance hull or one made for a surface drive.

The X dimension (motor height) will largely depend on what prop you run and how much set back. Different style props run at different heights.

I would think the standard push-pull cable (like Teleflex) would work fine. If it were mine I'd probably opt for the rack and pinion style rather than the rotary. Space permitting naturally.