Speed Question GT150

[Gordon02]

Guys, I'm 61 so I grew-up with 007 films. Live and Let Die is my favorite and has been since I was 15 and saw the movie 3 consecutive days in a row..

Ok, so what has all this got to do with my post? Since getting my own GT150 restore project in late August, I've been capturing images from photos and videos to aid me in the restoration. One particular video watched states that the record jump required 75 mph. I've watched the video several times now and nothing I've seen looks anything like 75 mph. I also don't buy the Evinrude 135 pushing the boat to that speed. Based on my math, even with a health 140 horse, 60 - 62 mph would be possible if the outboard could turn a 23" stainless prop 6,200 rpm.

Does anyone know or have that jump speed? Has anyone driven a GT150 to 75 mph, if so what horsepower did it take? Without a pad, I have my concerns that even 60 on one of these would be suicide.

I've owned an Allison XB2002/ProMax SS for 20 years now that is capable of mid-90's and I've owned dozens of boats that would do mid- 60's. None of the bassboats with 150 horses ever got to that speed. That claimed 75 mph is hauling butt! I have a hard time believing a cross-charged V4 and a Glastron GT150 ever got there.

On a humorous note, while watching those chase scenes now almost 50 years later - I see lots of editing bloopers...

Thanks, Gordon

[Hyperacme]

Glyn has done extensive research on boat and jump.
He would be the guy to ask.

Link to profile ..
http://forum.cgoamn.com/index.php?action=profile;u=37

[GT]

From a Glastron company press release...The GT-150 was going 56 mph for the jump with the 135 hp Evinrude. The chase boat measured at 54 mph - and barely cleared the police car.  gt

[Gordon02]

Thanks GT, this 56 mph makes perfect sense and is within the 135 hp's capacity. That 75 mph just caught my attention with certain doubts.

Best Regards, Gordon

[Gordon02]

I found this 1973 original article from the New York Times - Google is awesome......

"In making the jump, Comeaux drove a Glastron GT‐150 runabout, mounting a 135‐horsepower Evinrude Starflite engine. Boat and motor were tailored to the task. The boat is a deep‐vee 15‐footer, weighing 585 pounds.

Two wooden strakes were bolted to the after portion of its bottom. The strakes, equidistant on either side of the keel, were designed to keep the boat upright as it traveled up the ramp. This they did admirably, according to Comeaux. However, they also caused the boat to “surge” at planing speed.

Comeaux estimated that he needed a jump speed of 56 miles an hour. To achieve this speed and to decrease the boat's surging attitude, Evinrude assigned Ray Heurtin, a youthful technical adviser, to the film. Heurtin reached into a bag of tricks that has proved successful on the racing circuit. The first was to jack up the motor on the boat's transom. The second was to fit the motor with a cleaver racing prop.

The jack‐up was accomplished by through‐bolting an aluminum plate to the transom. This permitted the motor to be raised four inches above its normal transom height. The cleaver propeller is a surfacing prop. One half of the propeller works out of the water at all times. The combination of these factors tends to raise boat and motor from its element."

[Gordon02]

The raised propshaft height (4") and use of a Cleaver explain why the boat approaches the dyke (ramp we can't see) with absolutely no bow lift. I'd often wondered why that was since a flat attitude will increase wetted surface - slowing the boat from drag. Raising the engine reduces leverage needed for bow lift and Cleavers are stern lifting props - perfect explanations for that "bow down" approach.

I'm guessing too that those protruding strakes near the keel for balance on the ramp caused cavitation of the prop and was the source and cause of that surging mentioned in the article. 

Thanks GT, Gregg -

Gordon