TOPIC: lets talk jack plates

I keep reading about setting the motor back and rasing it with a jack plate. Besides running shallower, what could I realistically expect to see from building/adding a jack plate?

I don't know what a good a jack plate is except to put a long shaft motor on a short shaft transom.
Heres pic or 2 of one I made to put a long shaft bear cat on a G3
Mike aka the pirate
Ps
The was made out of 2in angle alumimum [img] [img]http://www.fiberglassics.com/media/kunena/attachments/legacy/images/PA260004-20110823.JPG

that brings up a question then... where should teh prop be in relation to the bottom of the hull? I'm running a long shaft on my g3 but I have a later model that I thought was designed for ls.

Besides running shallower, what could I realistically expect to see from building/adding a jack plate?

vertical travel isnt enough to really consider it for running shallow,

its a performance part the higher you jack up the motor the less resistance on the leg the faster you go, you get to a point where you run out of room to jack it up because you loose your cooling water, then if your after more speed, you continue to jack it up but you now need a low water pickup so you can affectively cool the motor and dump a load of cash on a Stainless Steel surface piercing prop

the setback provided by a jackplate will help launch the boat out of the hole considerably quicker which in turn is a gas saver , in some hulls it will help top end or gas consumption

if you have a hull that porpoise's sometimes jacking up the motor will relieve this symptom, however if the boats CG is so far off the setback will increase your problem, because your moving the weight of the motor farther from CG

jackplates available in , fixed position, manual adj, and power adj......& also in power tilt and trim

that brings up a question then... where should teh prop be in relation to the bottom of the hull? I'm running a long shaft on my g3 but I have a later model that I thought was designed for ls

general rule of thumb, the cavitation plate should be level with the bottom of the hull....this will always be a good starting place & satisfactory for most hulls, except for those performance buffs with that Need for Speed...see above

"if you have a hull that porpoise's sometimes jacking up the motor will relieve this symptom, however if the boats CG is so far off the setback will increase your problem, because your moving the weight of the motor farther from CG"

Strange this has come up, just last night me and two others were talking about stopping a porpoising problem. The g3 has a stack-6 and a heavy new Jack-plate with 5-6" setback. CG came up a few times and I'm not sure but suspect thats even a grater factor than the motor weight on the transom, as it increases the GC to the rear alot with each inch increased back, this is more of a question cause I'm not sure? Similar to Pathfinderz, Wade made a custom solid aluminum Jack plate to run a long shaft on a original transom, real nice design but you had to manually adjust it, its setback was no more than 2" from the motors original position. Wade didn't finished the boat so who knows the ride? I suppose he sold it as haven't seen him on the board in a while:(

g3bill

first approach to your problem is to move weight from the rear and put it up under the bow

tunnel hulls & small mini speed boats are really susceptible to this
and weight distribution is usually the key

I would think rather than adding weight, trim tabs could counter the CG effect, any thoughts on trim tabs... My 1st '60 g3 has a small set of old Step&Trim tabs and the ride was great even with a bad hook.

I never said add weight........RE-distribute the weight in front of the CG

trim tabs will help in some cases but scrub off speed

Ok, Shift weight toward bow, same diff kinda. on mine the gas tank was originally in the bow and now have two 6gal tanks under the CD. Some I know like Nut have power tabs to balance the Beer Keg load and lift tabs for speed. I had to settle for a happy medium with not too much down setting, pretty much even with the hull bottom. If I raise it a bit too much I will lose the lift to plane at slower speeds. Its fine for me though:)
If the CG is the big problem, why not put the battery under the center deck, in the middle between the tanks might be a good option? I haven't noticed anyone do this...

jet, though I have no need to run a jack plate on my G3s ,I do have a 14' cobra that....well it didnt do anything very well, turning was a hair raising experiance and it was twitchy the rest of the time. I was going to sell it but I first sold the engine a 115 merc. later i installed a jackplate on it and an 850 merc, WOW it was perfect, it handled great, the difference was night & day. later I installed a merc 1000 and it was fast as I wanted to go in a 14'er. see it on my youtube chanel if you wnt. "cobra time"

I sure dont think it would hurt your CG3 in performance or looks, I would run it about 2" above the hull to start with and adj as nessasary. i run the reggie 2" above and ugly peg 4" above but I also run chopper props witch need the air to get the spd I need.

lots of info to consider... I havent had a chance to look at my setup (working OT) but I think Im sitting a couple inches too low. I have 3-4" of adjustment on the motor mount without going to a setback/jack plate.

I've boated for prolly 15 yrs but this is the first I have gotten into performance boats. Always had junky ski boats that plowed thru the water at 35mph on a good day. Flying 3/4 of the boat is a new sensation that I like.

Jetboat

When you post on this board please remind us on which style G-3 you are asking about.
As you should know most of us speak of the early (classic) models either with the center deck or
the open model. Both G-3s have the sponsons and are the same boat (hull) below the decks.
The later model G-3s built when Larson purchased Glasspar are a different boat and
were designed for the long (20") motors. Which G-3 do you have? A long shaft motor on
the classic model will require a jack plate or rebuilt transom to 20+"

John

I have a larson era

John wrote,..."Both G-3s have the sponsons and are the same boat (hull) below the decks."

John,
Do you (or anyone) know for a fact that the bottom half of a G3 - whether center-deck or open cockpit - can accept the deck half from either models?
Wondering specifically if I can use my '66 open cockpit hull under an earlier center-deck top.
Thom

And in and effort not to high-jack the the jackplate topic,...I have just added a set of trim tabs or after-planes to Wild Thanggg in an effort to tame the wild romping in the mid-range.
I too believe CG & surfacing chopper torque play very active roles in handling.
This may be Wild Thanggg's last shot at breaking the sound barrier, because if this doesn't help I'm going to run a little 4 cyl Merc and simply enjoy the classic ride - before I thrash my G3.
I'm probably going to drop HP after my next run anyway.
My old carcass just can't take so much fun any more.
Thom

Yes Thom, you can put a center-deck top cap on a open deck lower hull. Any combination from 1959 to 1968 will swap out. All the G-3s from the Glasspar (Bill Tritt) era are interchangable. Can't interchange the later Larson verson with a Glasspar model.

Thom; I have actually made the swap between open deck and centerdeck hulls and caps on several boats now. While it can be done the transoms are shaped differently on the two models and some modification to the transom has to be made before they will interchange. The motor opening is larger on the opendeck than the centerdeck as is the shape of the curve so this has to be made to match up. Everything else is a good fit. Brian

Brian,
If I'm understanding you correctly,...
I would need to keep which ever splashwell piece that matches whichever top section I choose to use??
And,...Are you saying that the actual curve of the transom from port to starboard is different too?
Thanks,
Thom

hey that boat you two coots are standing behind was just in my driveway. I hope it is still running. Doh!

How was that boat in your driveway now!! It left Fl a long time ago!!

By the way, those two old "coots" are great G-3 and Merc owners/operators!!! And we have two G-3 driving co-pilots when afloat also!!

No thom the curve is the same for both transoms but the rise for the decks is different as is the width of the splashwell and the opening for it. Brian

Thanks Brian.

Thom

jetboat:

I installed a "Bob's Machine Hydraulic Jackplate" on the transom of our 1960 G-3 and could not be happier with it! In my opinion, it is one of the best things I have ever done to our G-3. In addition to being able to run in shallower water with it, it also gives better performance as MadProps explained in his posts. I was helped on my decision to go with the jackplate by Fiberglassics Member Kevin Sweeney. He has two (2) G-3's and has the same jackplates as I do with no problems whatsoever. I see no downside to installing a jackplate on any G-3 at all!

Good luck to you Sir!

I know I can't afford it but how much does that jack plate cost?
Mike aka the pirate

The manually adjustable basic models are just under $200 Mike, the hydraulic models run $400 - $800, depending on make and whether you get the tilt/trim unit too. They do pop up on Ebay once in a while as well.