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[Blue_Heron]

Originally Posted by PharmD2B31

If we were to add a bracket, I was wondering if you had to figure the bracket length into the total length of the boat......going from 19' 6" to 21' 6" if we were to add a 24" setback bracket???? This would move the center of gravity for the boat back 1-2" to 13-14' measuring from the bow of the boat.

This is the most important question to consider when you add a bracket. The bracket shifts weight and buoyancy aft, but once you're on plane, the typical bracket doesn't produce hydrodynamic lift. So it helps keep the scuppers above the water at the dock, but once you're on plane, it forces the hull's center of lift aft which hurts low speed performance.

Originally Posted by PharmD2B31

I know if I can calculate the center of gravity for the boat I can then apply foot pounds of downward force applied to the boat with however my boat is going to be set-up and optimize the center of gravity of the boat on weight distribution.

I think you're on the right track. Determine the correct location for the CG. Don't figure the bracket into wetted length, and use a moment equation to calculate the effect of engine, batteries, console, crew, etc. on CG.

Dave

[gofastsandman]

Originally Posted by Blue_Heron

Good. You scared me.



I believe the CG of planing hulls is normally measured from the transom heel (the point where the keel intersects the transom). It is usually measured as a percentage of static wetted length.

The static wetted length of a 20' Seacraft is about 17.5'. I've been told that a typical CG should be at about 33% of static wetted length, which would put the 20' Seacraft CG about 5'-9" forward of the transom heel. This is not gospel, just some preliminary calcs I've done preparing for my own 20' resto.
Dave

Carl said the cg was determined by the tank placement with different thoughts and ballast tank design. If you place the tank just a tad forward of the cg, you may find happiness.

I`m not allowed to ride wheels.

Cheers,
GFS

[Bushwacker]

Originally Posted by PharmD2B31

. . . So does anyone have the center of gravity numbers for a 20' Seacraft Center Console??? . . .

Being a pilot, Moesly understood the importance of CG location and it's effect on performance better than most folks. He generally installed the fuel tank right on the boat's CG (at least he did on my Seafari), so the boat's trim wouldn't change as you burn off fuel. If you assume that the boat's original CG (with a 300 lb motor) was about where the center of the fuel tank was, I think you would be in the ball park, at least for a starting point.

[gofastsandman]

He built a flying wing hull. How cool is that thought?

[PharmD2B31]

So I took the schematic on the SF20 off the specifications page from the front page and printed it out and graphed it. If it is true that Mr. Mosely put the fuel tank right on the center of gravity of the boat, then that rings true with what I was saying previous. The center of gravity on the 20' Seacraft SF is exactly 63% of the total length of the boat. That puts the center of gravity for the boat at 12' 4" from the bow of the boat. In all my readings for boat building, it was noted that most boats' center of gravity was somewhere between 60-65% of the total length of the vessel. This obvious rings true here as well.

Now I am going to try to apply foot lbs of downward force with regards to his layout of the hull along with the max recommended horsepower engine weight during that time this vessel was made and use that info to see what the weight ratios were and try to extrapolate that info to how I want to rig the vessel today.

[Old'sCool]

Originally Posted by PharmD2B31

Now I am going to try to apply foot lbs of downward force with regards to his layout of the hull along with the max recommended horsepower engine weight during that time this vessel was made and use that info to see what the weight ratios were and try to extrapolate that info to how I want to rig the vessel today.

Taking into account 4 stroke weight?

[PharmD2B31]

I will be looking at max hp 2 stroke weight that was originally recommended for the boat.

Once you find the center of gravity of a boat, you are supposed to be able to measure out foot lbs of weight of downward force on the boat as the weight moves away from the center if gravity of the boat. I plan on trying to figure out the most weighty objects in the boat and try to see what the weight distribution looks like.

Taking that info, I will then mock the weights of the new engine I am wanting to use and how I want to set my boat up and see what my weight distribution would look like and see how it relates to the original design set up. I can then move weight around in the boat to try to get as close as I can to what the weight distribution design was originally.

If you look at the two different spec sheets... One on the SF 20 and one on the Seafari 20, you will notice that the fuel tank is in two different spots. I don't believe this is due to the center of gravity changing because the center of gravity of the hull shouldn't change. The SF20 has a more open bow and is lighter in the front end so the fuel tank appears to be positioned near center of the boat. The Seafari 20 on the other hand has a more heavier front end due to the cabin and thus if you see to where the fuel tank is located it is located more off center towards the stern of the boat. Also of note was the use of a more lighter capacity fuel tank at 38 gallons. Again, I do not believe the center of gravity of these boats change.... Rather it's more of a changing of weight distribution around the center of gravity.

[Reelsknotty]

The boat in this video has the new f225 which should be the same weight as the f300. You might be able to get in touch with whoever did this restore to find more info on what they did to offset the weight if anything.
http://vimeo.com/67663992

Not affiliated, just happen to stumble across this video the other day.

[PharmD2B31]

Originally Posted by Reelsknotty

The boat in this video has the new f225 which should be the same weight as the f300. You might be able to get in touch with whoever did this restore to find more info on what they did to offset the weight if anything.
http://vimeo.com/67663992

Not affiliated, just happen to stumble across this video the other day.

That's what I'm talking about!!! I see too many Key West bay boats in my area with Yamaha F250's on them and they are not much larger than the Seacraft. I really see no reason as to why an F300 couldn't be ran on one.

I may have to give Tuuci a call and see if they would be will to give me the contact info for the owner if that boat.

Thanks a bunch!!!

[Reelsknotty]

If they don't, I bet caymanboy may know him.