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24' Grady-White slow top speed!

L

LX Kid

Regular Contributor
I have an "old" '82 Grady-White, 24 foot, walk around cuddy that seems a little slow to me. It had been sitting un-used for 3.5 years on the side of the house. Took me about six weeks to get her back in the water again. When I took her out for a sea trial I was only able to get her up to 30 mph wide open @5000 rpm if tach is correct. Speed was verified on my gps as well as the speedo. Seems like I remember getting 38mph before. I was wondering if anyone else has same boat to get a comparison with. I have a "Ballistic" prop but don't know the pitch on it. I removed the Carter carb, years ago, and put on a Marine 650cfm Edlebrock. GM 305 engine. The ethanol fuel "is" 3.5 years old and treated with Seafoam additive. Tried different trim settings up on plane.


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Maybe that's just the top speed for the old gal! Kinda like riding in a "Slow boat to China" as the saying goes. LoL
 
Was it covered up sitting on the side of the house? My floor and stringers were so wet and waterlogged that I could have grown a garden in it. The foam weighed pounds instead of ounces.
 
floatin radio said:
Was it covered up sitting on the side of the house? My floor and stringers were so wet and waterlogged that I could have grown a garden in it. The foam weighed pounds instead of ounces.
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No it wasn't covered. When it conked out 3.5 years ago I just got fed up with it and let it sit. A friend, about six weeks ago, told me he would assist me to get it back in the water again if I'd take him fishing! Several years ago I had the fuel bays rebuilt with new wood and fiberglass. Deck is also solid. Rebuilt the fuel bay covers also. All is good.

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Found the pitch marked on the back side of the prop. It's 14-5/8 x 15. Don't really know how that correlates to speed, power, etc though.
 
Just found specs where the "WOT" is 4200 - 4600 rpm with I/O engine ! I've been trying to keep rpm's down around 4000 due to engines age. Still doesn't mean much to me when selecting a prop that will give me top speed to go off-shore fishing. Loaded with 150 gallons fuel (950 lbs), equipment and 4 people I'm "guessing" that my boat would weigh around 6500 pounds. I read that the dry weight is about 4150 pounds.
 
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Basically the lower the pitch (15) equals higher rpms lower top speed.
Higher pitch (19) will lower rpms and increase top speed.

Typically pitch changes in 2 digit steps, 13, 15 ,17,19,21,23.

Typical is ~ 300 rpms per pitch change and maybe 1-3 mph.

So if you go to a 14.5 diameter and a 19 pitch it should put you at ~4400 rpms and maybe gain ~5 or so mph. Slower to plane off but higher speeds.
 
I would first confirm WOT rpms with a known good tach. I have heard the dole fin on the lower unit will create drag that is not necessary. You can try pulling it off and see if it improves performance.
 
I would pump that crappy 3.5 year old fuel out before you burn up that engine. Treated or not its no good at that age. And yes you will burn a hole in a piston.

Get some good Marina supplied fuel in the boat and retest. It will run best on 87 octane.
 
kimcrwbr1 said:
I would first confirm WOT rpms with a known good tach. I have heard the dole fin on the lower unit will create drag that is not necessary. You can try pulling it off and see if it improves performance.
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I just bought an RPM/Dwell gauge to check my tach and point dwell for accuracy. Have some new points and condenser to put in also. Already changed the plugs out.
 
After you set the dwell (point/gap) then check/adjust the base timing. Then check the progressive timing advance is within spec. Then you can adjust prop pitch for proper WOT rpms.
 
Docksidemarineservices said:
I would pump that crappy 3.5 year old fuel out before you burn up that engine. Treated or not its no good at that age. And yes you will burn a hole in a piston.

Get some good Marina supplied fuel in the boat and retest. It will run best on 87 octane.
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To late! Already put "Sea Foam" and "FX Gas Treatment" in both tanks and filled rear tank. Both tanks were about 1/4 full of old gas. Already been out fishing/sea trials several times.
 
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