Height of motor on transom

[Nauti & Nice]

This is related to Info. that I picked up on mac26x list last year.
A 2002 26X out of Tallahassee, Fl. had his motor dropped so that
it fit the mounting bradket down on the to edge of the transom.
Mine is one inch higher. The Florida boat is running a 11.75 x 10
prop. #581-30-zv5-860za. Both our boats have Honda's.
Hugh is running 23 mph by gps. I'm not even close. The prop
I'm running also came from info off the mac26 list site, 12x10.
any ideas?

George
MacX4531f101

[Timm Miller]

Mine also sits down on the bracket and I'm am loaded down for cruisng and can get 18 with the wind and current behind me. 23 would be possible with no load or fuel or rigging. How is your WOT with your current set up?.....lower end of 5500 or towards the the top of 5900? I'm running a 4x11.5x8 prop and can get mine up to 5950.....so that tells me I'm dialed in pretty close. It's not a matter of speed but the rpm's that are important to each and every setup. Having it dialed in towards the top allows you to add more wieght or gear and still be in the range. If you want more top end, get a bigger motor......there is no replacement for displacement.

[Sloop John B]

I have always read and thought that proper motor placement had the cavitation plate even with the bottom of the hull. With this, the bracket should have some gap.

I never heard of a Mac going 23 mph, except for Rogers stripped down greased hull from the video.

[Timm Miller]

My cavitation plate is about 1 inch below the hull.

[HERNDON]

I leave my little 8 hp down when sailing as the cables for the engine, when in the up position seem to interfere with the steering. for the rudders.

Rob H.

[Frank C]

Not to sound smartass, but my outboard weighs 335# (Suzuki DF60) and required an engine hoist and two persons, one doing a belly crawl to the inside transom when mounting it. So raising or dropping it by an inch is not an average Saturday morning performance whim.

Besides, the difference couldn't be more than one mph or so - would anyone care? I never run my motor flat-out. Why waste the gas? I try to optimize for a quiet, mid-range cruising speed ... about 16 mph @ 4000 rpms, while WOT is 21 or so.

The principle in motor placement is to minimize drag (shallow as possible) while avoiding cavitation (caused by the prop thrashing too close to the surface). The idea is to provide relatively clean water flow to the prop. Mine is set so the cavitation plate is about 1/2 inch below the hull. It still cavitates sometimes in sharp turns, so raising it isn't in the cards.

[mike]

There's a gap between my bracket and transom (haven't looked closely... I'm guessing it's about an inch, maybe less).

If I did someday want to try moving it down, does that require drilling new holes in the transom? Or can the existing holes be used?

--Mike

[Terry]

About those propeller sizes, sound like Tim is dialled in pretty close. I found a propeller calculator at some site about.com the link is here:

http://powerboat.about.com/gi/dynamic/o ... Fprop.html

I put in Tims' prop size and rpm and speed using the Honda 2.09:1 ratio and it calculated only 15% slippage. Mine came out 35% slippage because I have not yet had my 4X11.4X10 prop pitched down to 8 like Tim's. It would be interesting if everyone was to try this calculator out and find what the slippage comes out to and post it giving your engine type & size and the data used so we can all see who has the best setup for the boat in question. Any takers?

[mike]

Existing holes usually work. Typically, it's just a matter of going up or down, 1 or more notches on the bracket.

Yes, I took a closer look at it today and discovered this. However, I also noticed that the starboard side of the bracket is about 3/4" off the transom, while the port side is on the transom! The bolt is going through the same hole on both sides (3rd from the top, I believe), but one bolt is a little higher than the other. So, my motor is tilted slightly. Eeeek!

--Mike

[Joe 26M Time Warp]

I installed my honda 50 directly on the transon, I drilled though the transom and installed bolts. When I raise motor to sail all my cables seemed cramped and rub. I saw another 26X with about 3" gap between transom and motor. when motor is raised it rotates with less rubbing. Removeing the motor from the rudders, when sailing is just too much work. If I had to do it over agoin I would raise it so that the cavatation plate is equal to the botom of hull.

I still haven't installed the motor on the new Time Warp yet. My plan is to simply install the same aluminum 1/8" plate on the transom where it was on the (hull #32) 2003. From there, I'll use either aluminum channel or square tube for an adjustable mount that extends the motor back at least 3" from the transom.
I'll be able to change the height of the engine by wrench for tuning. And I'll find a better way to bend those stupid engine control cables right down into the hole where they belong.
Of course, for this season, I'll probably just mount the engine the same old way and play around with it if I get the chance.

[Joe 26M Time Warp]

I have always read and thought that proper motor placement had the cavitation plate even with the bottom of the hull. With this, the bracket should have some gap.

I did some research on the subject last fall and got basically the same answer; 'cavitation plate even with the bottom of hull', from dealers & the Mac factory, although Bill @ the factory worded it "at or about 1" below the bottom of the transom. The Honda manual says even with the bottom of the hull. On the 26M, and I assume the X, one onch below the transom is going to be almost exactly even with the bottom of the hull.
Several things got me interested in the height of the motor, one of those was the fact that I get some ventilation even though the engine mount is as far down on the transom as it can go. I.E. The safety tabs that would hold the engine in place if all the bolts were removed are / were already in contact with the transom. No adjustment downward is possible without spacing the motor far enough from the transom to clear those safety tabs, or cutting them off.

Although I regard and respect most of the physical shapes and relationships nailed down in Roger's die set, it wouldn't surprise me to find a true engine height sweet spot slightly beyond (or below) what the factory gave us to work with.
Perhaps more so on the M than the X because of the redesigned bottom and potential to overlook a newfound hydro-dynamic smoothness the X with the centerboard disturbance was never capable of.
Obviously I'm talking minor differences and refined performance tuning that might only provide a 1 mph difference, but we climb these mountains as much "because it was there", as anything else. Besides, this should be interesting.

[Frank C]

I bought the Mac to learn sailing and to get out on the water. I have an E-type Jaguar for scratching the speed itch. The water usage model for both motoring and sailing in the Mac are not too dissimilar. I oversized my Mac's motor (DF60) simply because I wanted to reach a comfortable 15 mph cruise, without having a screamin' eagle on my shoulder. I know it's slightly over-propped at 13" pitch, but it's not worth my effort, time or expense to fiddle with it. I'd rather use it, as is.

( EDIT: btw, the realities of sail-racing the Mac are about the same. )

"Sedate" is a good word to describe the Mac. IMO, tweaking and tuning isn't impossible ... neither would be blueprinting a Toyota Echo, but why bother? Trying to waterski w/ a Mac is a little like revving your Echo at the stoplight (look around for the polite smiles). With all due respect, if you're sating a need for speed, the Mac ain't the right vessel.