Originally Posted by Locozodiac
2 issues: (1) are you towing the boat & engine on a trailer ? Or on sea by another sib/Rib ?
Most dealers have advised against towing the boat with the motor mounted on the transom due to the pressure applied to the transom during transport, especially over long periods and poor roads
Hopefully he's towing on a trailer. As "super" as the Merc Super 15 is, I doubt is has the power to propel the craft for too long or too far over a bad road without help.
The big thing is to limit the amount of fore-aft force applied to the transom on rough roads. Most of that force comes from the pendulum effect of the motor. Since it's that kinetic energy imparted to the motor mass that you (or the dealer) is concerned about, you need a transom saver. Basically, it's a support bracket that transfers load from the engine to the trailer.
Here's one of the cheaper commercial alternatives: http://shop.easternmarine.com/index....productID=6325
The rubber V block cradles the motor's lower end, and the other end of the shaft goes to the rear trailer cross-member (either cradling a roller, or to a bolt-on bracket, depending on what you have on your trailer.) This particular unit has a spring-loaded section, so it compresses a bit as you lower the motor onto it. Note that I do not endorse this particular product (mine lasted something less than a year before it rusted into uselessness); it's shown as an example. You can fab up something similar for *much* less money. (The spring, IMO, is superfluous, and something akin to a wooden block with a bit of carpeting would do for the rubber V-block.)