Trailering boat with motor or not?

[Buccaneer]

Do you guys trailer you vintage AlumaCrafts with a motor attached to the transom
on longer trips? I’ve had a few newer, bigger boats with bigger outboards, and
they had the transom saver bar to keep the motor from bouncing, etc.
Just read a 1960 article in Popular Mechanics on aluminum boat repair.
They mentioned "cracks", "leaky rivets", etc., from the weight of the motor
on the transom as they’re being trailered and bounced down the road.

Let’s say I’m thinking of taking my 1959 AlumaCraft AL-14′ on my Gator trailer with
those little bunks and a 40 pound outboard on the transom, about
300 miles to Tomahawk, and there won’t be much room in the car or
elsewhere in the boat to store it……. does the transom survive the
Wisconsin potholes?
Thanks!

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Attachments:

Prepare to be boarded!

[mr-asa]

I’ve been thinking about this as well, as I’m getting to a point with my Herter’s that I’ll be able to put it in the water regularly with a 25HP on it. If you’ve got a light motor, it might be ok, but if not I don’t know that it would be a good idea.
A lot of it depends on the overhang of your boat from the bunks. The more of the boat that isn’t supported the worse it will get. Even the 15" up for the transom can do some damage if you’re hitting a lot of bumps and shaking it around.

With that motor I think it will be ok, if you put a 15-18HP OMC from the mid to late 50s on there, I don’t think you’ll like the long term results

[david-bartlett]

Buc,

That little motor won’t hurt that boat at all.

[johnyrude200]

2 words regardless of how ridiculous it may look, or sound.

TRANSOM SAVER

The weight has a factor, but remember that force = mass x velocity (from my days studying biomechanics).

So even though your little 3hp motor may only weigh 30 pounds, when you’re driving 60mph and hit little bumps, or a gust of wind, that force is transmitted to your transom.

I mean, a .223 caliber bullet flying at 1200 feet per second (FPS) is enough to blow a hole in 2 inch thick piece of concrete at 100 yards, or a 1/2 inch thick iron plate…and that only weighs an ounce at most. Just physics at work.

Mechanically support your motor regardless of how far your trip is. Those aluminum rivets (or even a fiber glass boat) don’t need any extra abuse.

[mr-asa]

Johnnyrude, I was more thinking of the flexing caused by a moment from the motor moving around.

[johnyrude200]

You’re spot on…that flexing is physics. It’s like taking a flat piece of sheet metal and applying force to one edge (not to get heady) in a way perpendicular to the horizontal surface. Point of axis is the tires…lever is length from that to the aft of the motor…longer distance equals more force, but I would consider the rivets of the transom to the be the axis point, even though the lever is short.

The X factor is the momentum of the vehicle and flex of the vertical transom with weight. So technically the moment arm is almost nothing, perhaps 1/4-1/2 inch flex of the transom, but with such a light material and the introduction of velocity, just isn’t worth it in my opinion. There are many structural mechanics converging at once on a transom, but keep in mind the material is aluminum and generally 1/16th – 1/8th in thickness. Not that beefy.

Just imagine the way glass installers move a mirror…they carry it vertically…NEVER horizontally…because the strength is along the length/width, never the DEPTH.

A transom with a motor is the same idea…force being applied to the depth when forward movement/displacement is introduced (i.e. driving in ANY direction).

I have repaired/replaced so many stern brackets for the broken motor mounts due to customers transporting their motors to me without a transom saver. I admit, I almost constantly look at my 2014 etec (30hp on a 2001 14′ aluminum starcraft…tiller) and watch the motor ‘snapping’ back and forth every time I jump a wave or chop. I wonder how long before the rubber motor mounts snap in half. And that motor is 182lbs…not a light motor at all!

If you want to have some fun thinking about physics, think about how easy it is to lift your bow when you have all your gear in the back on a trailer. That’s a 1st class lever (pivot ponit is the trailer tires), basically the same as a see-saw. Try lifting the bow in the same situation by moving closer to the boat, away from the tongue. It will feel much heavier the closer you get.

We all use ‘cheater’ bars when trying to pull flywheels? Why? By increasing the lever arm (the longer handle), we put physics into our favor from a mathemetical standpoint. The pivot point is the center of the crank. The further distance you get from the axis point, the greater the mechanical advantage (or lower the disadvantage).

[frankr]

I don’t have an Alumacraft (well yes I do–a jon boat). But I do have a 14′ Lund aluminum with a 35hp on it. It’s so old nobody can date it. And I’ve towed it with the motor on from FL to Canada twice, and to Northern Minnesota. Also countless other trips like Georgia etc. Even more, I’ve abused that poor thing a LOT. Bottom is all dented from hitting logs and rocks. It just keeps on keeping on. No leaks. I did replace the transom wood a few years ago because it just rotted out. These things are tougher than we give them credit for. Disclaimer: If it was as nice as the rig in the picture, it might get treated with more respect.

[johnyrude200]

To frank’s point…I’m pretty sure the old vessels were made WELL before computers were used to calculate physical limitations of various materials and things were engineered to be used and abused AND last. I.E., mid 50’s motors use springs instead of rubber as motor mounts.

There’s a reason whey they are still kicking around, they were over engineered because people (I surmise) weren’t skimping on materials to just ‘get by’ during production. They were way more beefier than needed due to the lack of general tolerance calculations, not due to lack of craftsmanship. I could be wrong though?

Still interesting to think that an iPhone has thousands X more power than the worlds supercomputer of the 1960’s.

[chris-p]

The force put on the transom when accelerating on the water from a dead stop is far greater than anything encountered trailering around. that little guy wont even be felt by your boat, but by all means, a transom saver, or removing it for the trip, obviously wont hurt anything.

[billw]

I have made a number of long trips (200 miles or so, each way) to meets, with 15 to 18 hp motors on the transom of a 1993 Mirrocraft. The transom is much better-built than my Alumacraft’s transom ever was. At first, I would wreathe in agony, looking back at just how badly those motors would thrash around on the transom. The boat did develop a leak; although it is anybody’s guess whether it happened in the water or on the trailer. Anyway, I started tying the motor down: both side to side and from trying to move in the tilting arc. It certainly seemed to trailer better, that way. I think this cuts down on Johnnyrude’s F=MA equation….it cuts down on the hammer effect.

A long time ago, there was an article in the Outboarder about putting shocks on a boat trailer. This seemed like a really good idea to me; however, I could not figure out how to calculate for, then find, the right shock for the load range….So I never did it.

Long live American manufacturing!

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