Cajun Engineering

[Reese]

Built a 9” stationary setback to go with the 5 ½” CMC and needed to know how much the transom would flex.

I started wondering “what would those byuboyz do facing this type of predicament”…easy bolt on an old 18” swim step and start jumping on the end of it.

The whole mess ends up about 32” away from the transom, my big butt weighs about 220 so the math is 220 x 2.66 (32/12) + 220 = 806 Lbs of down force on the transom! This is almost the exact force a 375 Lb outboard would generate on a 14 ½” setback.

Got on the end of the swim step and started doing the up and down thing and measured less than 1/4” flex on the transom edge. Figured if it could hold up to my big ass maybe it will hold up when the real thing gets bolted on...hope I’m right.

[Flat Out]

1.Ol' T'Rex be proud a ya.
2.I've seen some biguns that would step on the ladder and sink that boat in a second.
3. You could put one of them enviromentalists back there and tell them to kick like hell.
4. Some fancy kicker motor braket.
Be aware its not only the weight, but the amount of torque the motor produces and the force on the transom when you nail the throttle from a dead stop. Basically the whole boat is being lifted by the rear end so to speak by the motor. A transom can never be strong enough.

[Techno]

Is it possible for the board the jack plate is bolted to, to rip off?

From the pic it doesn't seem to have any support.

[T-REX]

Dats California redneck if I ever seen it...Now dat transom sho lookz purdier den it iz strong...I don't thank U gunna have no problemz at all, unless ya put sumpthin bigger den a 5hp on it...Maybe U should stick ta build'in cabinets, befo U git wet...REX:cool:

[Reese]

Now T…yu knos I was just fun’in, and getting wet is mo better dan build’n dem cabnets.

The picture looks like 9” backset is being supported by a very thin ¾” piece of ply on the transom. Believe me, 220 Lbs 32” from the transom jumping up and down, that back end would snap off like a twig.

I’ll have to take a picture from the inside of the boat to show you better, but the 9” backset is a one piece unit that extends and ties into very beefy stringers (2 ¼” thick x 7 ½” tall…it’s kinda a knee brace, stringer system all in one.

This entire backset and bracket were designed from the very beginning to carry 100% of the load, the rest of the transom has no load carrying function what so ever.

[ratso]

I would feel much better if it was made out of aluminum and bolted to the transom, not saying that your idea won't work, but our business is fiberglass, aluminum fabricating, etc., I would just be leery about putting too many HP's on the back of it.

[Backfire]

Reese
Lets see here, a l966 100hp Johnson will put out over 1000 lbs. of THRUST, as in try'in to twist the top off the transom. Now your
engine will do a bit more, 'probly more like 3000-4000 lbs in static
max hp thrust. With a large pitch prop at less than max rpm it will be a lot less but it will be way more than anything (806 lbs.) you are talking about- dead weight on the trailer. Plus there's them torque multipliers like props comming out then in the water,
g-forces, pie are square type thangs. Just wanted to see some real numbers, good luck and take a picture before you go to the lake.
Backfire :p

[Bob T]

Jist don't be hitt'in any bumps on the way to the lake or you'll be watch'in yer black beauty gett'n some road rash.Gettin to the lake can do way more s#*% .to your transom/bracket than any thing you do on the water.Ibuilt a 6'' setback from 3/8'' aluminum DOUBLED UP! Unless yer way sure............be REAL CAREFUL!!!!

[Techno]

You can't tell from the pic how its loaded. It sounds like the transom is like a false transom and the setback is the real transom, something like an STV.
Reese you've got everyone wondering now. Is it cheese?

[Reese]

Your right Techno…it’s the cheese…and the 3/4" transom is a false transom, the real transom is the 9” setback. I can see how that picture looks sort of funny and flimsy.

I appreciate everyone’s input…I know your basic concern is safety, let’s face it having the back end of your boat come off is not pretty. This design is many times stronger than the original which carried a 2.4 with the 5 ½” setback for more than two years.

B&WB did an article comparing engine torque and setbacks…the torque numbers are very similar to yours Backfire. But those figures are not instantaneous; they are applied over time 0-70MPH and with a tremendous amount of slip at the start. Trailering forces on the other hand are close to instantaneous (less suspension travel) especially hitting a bump going 90 down your favorite back road…guess that’s why they sell so many transom savers.

[Bob T]

Came home from work tonight ready to look through my old B&WBs for that article.Your second post cleared it up.Feel better now...saved me look'n fer hours.Be safe.B.T.

[pyro]

We want video of the maiden voyage.