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Author Topic:   88 Montauk- 100 GT Johnson-prop suggestions
bocaspiff posted 08-15-2002 07:54 AM ET (US)   Profile for bocaspiff   Send Email to bocaspiff  
I just bought my fifth Whaler last week, above referenced. Anyway, I used to have a 17 Newport with a 115 Yamaha and I ran a 19" stainless but I don't think the GT will spin that prop. The GT has shaved heads so it's pretty hot as it is. I'm a big fan of C-wave, I've been boating in Boca Raton for 20 years.
Bigshot posted 08-15-2002 10:39 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
A 19" on a 100 should be fine with light loads but a 17" double cupped stainless should be fine.
bocaspiff posted 08-15-2002 10:42 AM ET (US)     Profile for bocaspiff  Send Email to bocaspiff     
A response from BigShot! The royal treatment on my first day. I have a 17" SS with cupping now, I will try a 19" raker this weekend. Thanks sir.
PSW posted 08-17-2002 05:25 AM ET (US)     Profile for PSW  Send Email to PSW     
I have a GT100 and use a 19 pitch attwood ballistic prop and it runs great and has exceptional top end. If you want the hole shot for skiers or whatever else I would suggest a 17 pitch.
Dunk posted 08-21-2002 08:31 PM ET (US)     Profile for Dunk  Send Email to Dunk     
What year is that GT100?? Is she a bubble back or a flat back V4?? If she's flat she's probably running the small 1 1/4" carbs instead of the old 140 1 5/16" carbs. If she's running the small carbs you don't want to twist her over 5300 because she'll lean out on you above that rpm.

Any of the 16'7" whalers need the bottom straightened on them if you want it move. They are built with hook in them which makes them tough to trim up. If you can't trim and fly the boat you'll never see 50mph.

I had a 73' with 86 110hp Johnson. The 110's were 140's that got rerated in 86 at the prop. 140's never put out more than 128 at the flywheel on their best day, so figuring 6-8% drop at the prop the 110 was born. The 110 was about 122 at the prop which got in under the +- 10% NMMA leeway rule.

Before I blueprinted the bottom the boat would run 47-48 on the GPS twisting 19 Stiletto at 5200. After the bottom was right with the same prop at 5600 she would touch 53 on the GPS. The trim response difference was unbelieveable. Anything over 5000rpms with a little trim you could actually fly the boat. Once you cross the 50mph mark in those boats you get into a chinewalking problem. They like roll back and forth on that round bottom.

My brother still has the boat and is thinking of getting rid of it. I was thinking about buying it back, but I would put V6 and Bennett trim tabs on it if I did.

acassidy posted 08-21-2002 09:24 PM ET (US)     Profile for acassidy  Send Email to acassidy     
Dunk, how do you tell if the bottom is not straight. And how did you make it straight again. I know about blueprinting but I did not know that blue printing could evolve flattening the hull out. (Are you the same knowledgeable DUNK from the WMI board?)
masbama posted 08-21-2002 11:11 PM ET (US)     Profile for masbama  Send Email to masbama     
Welcome Dunk!
People-we are graced by cyber royalty!
Dunk is a generous, knowledgable poster.
Again,welcome Dunk!
Dunk posted 08-22-2002 12:41 AM ET (US)     Profile for Dunk  Send Email to Dunk     
Yes, I've done several whalers bottoms. Forget doing this right unless you flip the boat over. Just lay a 6ft straight edge along the bottom about ft out from the keel paralell to it. I've seen as much as 3/8" of inch of daylight over a two foot lenght of the straight edge starting 6" from the transom going forward. This hook vary's on different hulls. You need to fill this area. The hook works just like dragging trim tabs in the down position. Lots of boat manuf's build them into their hulls. It makes the boats plane easier with less hp and it stuffs the bow to make them safer and more controlable with the max hp.. Unfortunately when you wet more of the boat bottom it slows them down.

The gelcoat must be ground off down to the fiberglass. I used epoxy/cabosil putty to bring the area up flat. Takes allot of filling, waiting till it sets then sanding with belt sander. Sanding and checking with the straight edge. After that two coats of epoxy resin to smooth the whole area then some more sanding to bottom paint. One boat I covered the whole area with 1.5oz fiberglass cloth, but I don't think it's needed.

Yes, I was over here from the WMI/FL Sportsman board trying to get info on a 29 Outrage electrical system and saw some interesting post's. I just can't pass up getting in making whalers run. In fact the 17ft Mako I have now is putting me to sleep and I still have this itch to V6 a 16'7"...

bocaspiff posted 09-20-2002 03:43 PM ET (US)     Profile for bocaspiff  Send Email to bocaspiff     
I have a 1990 GT 100, flat back, tried 3 diff props,
13"x 19" SST= 45 mph
13.5"x18" Raker: over-revs but planes so fast its scary
21" renegade (4 blade): 51mph @ 5100.
Am I going to hurt the motor running the 4-blade b/c top end is a little low?

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