Heavier GF16 having trouble getting on plane

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AndrewS
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Heavier GF16 having trouble getting on plane

Post by AndrewS »

Hello, I finished building my GF16 last year and have taken it out a few times since then but have only managed to get on plane once when we were on a river and it was near glass flat. I used 1708 and and 2 extra gallons of epoxy or so when building the boat so I think it is probably heavier than the original design. I tried adding a doelfin but that did not help nor did an adjustable jack plate. I have been reading through some posts about the gf16 and have seen where people have swapped the prop and had better luck getting on plane. The boat has a 20hp merc 4 stroke efi motor on it and I am not 100% sure if something like this 10 pitch prop is what I should try out : https://www.nettleprops.com/store/p/876 ... rcury.aspx

Any help would be appreciated.

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Re: Heavier GF16 having trouble getting on plane

Post by Jaysen »

There is a good prop guy here... Tomw1. He can get you the spec on the right prop, but he will need some info.

What's the total weight of the boat AS YOU BUILT IT including all the cargo you would carry?

1. If you have a couple medium guys, food, drink, fuel, ice, bait etc. add that up.
2. Take the boat on a trailer to a scale and get it weighed. Then take the empty trailer to the scale and weigh it (if you have an unmodified trailer look for the weight on the manufacturer's label to avoid a second scale).
3. Add those two numbers. This is your total weight.

As much as we think we can use material used, it really does need to be weighed on a scale.
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Re: Heavier GF16 having trouble getting on plane

Post by Fuzz »

20 hp should be plenty to get that boat on step. Plans only call for 15 hp. Post a picture of how the motor is mounted. I am thinking it is mounted way too low.

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cape man
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Re: Heavier GF16 having trouble getting on plane

Post by cape man »

Actually you subtract the trailer weight, not add it. :lol: Jeff does the books and the pricing I hope! 8) :D

What prop are you currently running? Pics of the motor cavitation plate and the bottom of the stern would be good too. Agree with Fuzz. That motor should be plenty.
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Re: Heavier GF16 having trouble getting on plane

Post by fallguy1000 »

AndrewS wrote: Tue Sep 06, 2022 2:19 pm Hello, I finished building my GF16 last year and have taken it out a few times since then but have only managed to get on plane once when we were on a river and it was near glass flat. I used 1708 and and 2 extra gallons of epoxy or so when building the boat so I think it is probably heavier than the original design. I tried adding a doelfin but that did not help nor did an adjustable jack plate. I have been reading through some posts about the gf16 and have seen where people have swapped the prop and had better luck getting on plane. The boat has a 20hp merc 4 stroke efi motor on it and I am not 100% sure if something like this 10 pitch prop is what I should try out : https://www.nettleprops.com/store/p/876 ... rcury.aspx

Any help would be appreciated.
You really need to know if the motor is achieving max rpms. If the prop pitch is wrong; the engine nevers revs up. But TomW1 knows the configuration well enough to spec it close.

What prop is on it now?

Another issue could be if you built in some hook...this is easy to check for as well.
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Re: Heavier GF16 having trouble getting on plane

Post by TomW1 »

Tom here I will be glad to help you. As Jaysen said I will need the total weight of the boat as it leaves the dock.

Weight of boat:
Motor Merc 20HP 4st I will get the specs I need from there web site
Gas tank gal x 6.3lbs
People weight =
Gear: weight coolers. Ice, fishing gear, and any other things you carry onto the boat
Safety gear 50lbs
Other: Anchors, ropes spare parts like a prop and toolbox.

Be as close as you can with the weights as they are the most important factor in my calculations.

I have been on a GF16 and know you should not be having the problems you are. What size prop do now have? With a 20HP you should have a top speed in the mii 20's or slightly higher. On the GF16 I was on it had a 25HP and we reached the low 30's with two big guys on it. Make sure you have the cavitation plate is even with the bottom of the boat as the others have said.

I am getting ready to go on vacation so it may be next week till I get back to Io you.

Tom
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Re: Heavier GF16 having trouble getting on plane

Post by AndrewS »

Thanks for all the replied. I won't be able to weigh it until this weekend. The prop that is on there is a 3 blade and it stamped 10p. I made sure there wasn't a hook on the bottom before we flipped it. Here are some of the photos I was able to take. The top of the cav plate seems dead in line with the bottom of the boat. https://photos.app.goo.gl/MTBUFpYKkaqhaSJm9

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Re: Heavier GF16 having trouble getting on plane

Post by Evan_Gatehouse »

Can we assume the prop hub isn't slipping?
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Re: Heavier GF16 having trouble getting on plane

Post by AndrewS »

I don't think so, it seems like its pushing water fine, how would I check exactly?

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Re: Heavier GF16 having trouble getting on plane

Post by joe2700 »

AndrewS wrote: Wed Sep 07, 2022 8:29 pm I don't think so, it seems like its pushing water fine, how would I check exactly?
One option is to put a mark on the prop and the hub, use the boat for a while, then see if they still line up.

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