engine hieght on bracket

hugo · #1 01-14-2013, 03:41 PM

This is for those of you running a bracket on 20 footers?
So i know the rule of thumb in 1 inch up for every 12 inches back, but i think i remeber seeing somwhere that seacraft hull desighn actually likes the motor a little higher whether it be on a bracket or on a regular transom. So i was hoping some of you guys with brackets could give me real numbers on your setups.

I just finished my setup but havent had it in the water yet and wanted a good starting point for engine hieght, i have a 20 SF with 26 inch set back bracket. I was thinking 2.5 inches but i think somewhere i saw someone was running 3.5 inches up with good results. So what do you guys think?

McGillicuddy · #2 01-14-2013, 05:36 PM

My anti-cav. plate at 1-1/2" above keel. About perfect on my Seafari transom with 300 lb motor.

I think adding specifics like the motor/weight of the motor, and the type/make of the bracket would be helpful. The type of prop you will use also affects the height.

I think Bushwacker's was up around 4.5" with a Hermco 30" setback and a 420lb E-tec on his Seafari.

My guess is 2-1/2" won't be enough.
Heres a link to some other perspectives
http://www.classicseacraft.com/commu...height+bracket

Bushwacker · #3 01-14-2013, 06:51 PM

Close Gillie! Since I took that picture in the other thread which showed the AV plate at 3.25" above the keel, I had Don Herman redrill the motor mount holes on the bracket to raise the motor another inch, so it's now 4.25" above keel. Handling is fine, with no tendency to blow out in hard turns, and water pressure is also fine.

The basic objective in setting motor mount height, regardless of whether motor is hanging on the transom or on a bracket, is to have the AV plate above the water when you're up on plane with the motor trimmed out to your normal cruise position in order to minimize drag. It doesn't have to be dry but it should be clearly visible above the water, per recommendations from both BRP and the Merc Verado folks. My AV plate is still not quite out of the water, so I think it needs to come up another inch. However that will require something like a jack plate, which would increase setback even more and further screw up my CG which is already too far aft, so I'm looking at some sort of 1" thick spacer plate. I only saw about 50 rpm and maybe 1 mph gain with the last 1" raise, so it may be that I'm already close enough, but as an old jet engine performance engineer, I can't resist tweaking it more until I'm sure it's optimum! The only way to know that for sure is to go too far and then back up! You do have to keep an eye on water pressure because that can be a problem if you raise it too much!

hugo · #4 01-14-2013, 07:43 PM

thanks guys, im a little worried now because i set the bracket as low as possible to get the most amount of fotation i could get and im at 2.5 inches up above the keel now with only 1 hole left to go up. from what you guys are saying i need to take it to the last hole up and pray it is enough! its only 3/4 inch per hole so id be at 3 1/4 inches up. as for props i have a mirage 19p i was going to try and also a ss michigan wheel 19p or the old faithful aluminum black max 19p as well.oh and im using a miami stainless marine bracket. i sure hope its high enough.

workinpr0gress · #5 01-14-2013, 08:00 PM

Take it up to the top then go down if needed imho. Your bracket's about the same as mine and mounted about the same. I have no tabs. Your motor weighs about what mine does. Sometimes I feel like it could go up a couple more holes if they existed. I wish I had a little shorter bracket and a Jackplate, but not till my transom needs redoing.

hugo · #6 01-14-2013, 08:20 PM

thank i was just comparing pictures of our boats and they are close. i am going to raise it to the last one befor taking it out and hope its good. i guess with a 26 inch set back i could add a jackplate if i needed it. Oh the joy of spending my kids college money!

hugo · #7 01-14-2013, 08:27 PM

workinprogress are you still at 3" above the keel? and is that a good setting?. most the guys with brackets are not running center cousol and im wondering if thats why they can run the engine as high as they are. they have more forward weight im thinking.

WildBill · #8 01-14-2013, 08:34 PM

Has anyone tried a 20'' shaft on a 20 footer with a bracket? I do remember a few post's about the concern's of keeping the powerhead up out of the water by using a 25'' shaft length, but in this application on a 20 footer you could keep the bracket platform a little closer to the water line and you should have plenty of room to get your cavitation plate up higher and the powerhead should be high enough since we are talking about shaft length.
It appears that your initial set up of height on the transom side of your bracket is critical in dictating the size of shaft length with the height of bracket and placement of your bracket when mounting it to the hull.
Hugo, your last hole appears as if it will be pretty darn close.

good luck bill

hugo · #9 01-14-2013, 08:42 PM

Thanks Bill, thats what im thinking and hoping, im gonna move it and pray im good, i guess that because we have the VDH desighn hull it allows more water to flow back and fill the void behind the boat quicker than a traditional hull making us have to raise the motor more. hell i dont know , just speculating.........

workinpr0gress · #10 01-14-2013, 08:59 PM

Quote:

Originally Posted by hugo

thank i was just comparing pictures of our boats and they are close. i am going to raise it to the last one befor taking it out and hope its good. i guess with a 26 inch set back i could add a jackplate if i needed it. Oh the joy of spending my kids college money!

200hp Merc on the bracket mounted in the top hole would make me smile! The hydraulic jackplates have some weight that has to be accounted for. I would stay away from the hydraulic jackplate at our setbacks and volumes.

The setback and the volume of the bracket and engine choice are all important. If and when my old crossflow grenades I want to shorten my bracket to about 17-18" taking into account the jackplate thickness. Then I'm going to cut, weld and widen the chamber. The one advantage that the aluminum brackets have, especially with a small or no platform is weight. I really like the v6 eagle series carbed OMC's and I'd try to find a 175 of one of those if and when it's time.