Introduction: Jack Plate for Outboard Motor


Small boat from the 1950's made for short shaft outboard engine equipped with a long shaft engine which results in suboptimal performance and handling. Easiest would be to cut out the transom and rebuild it with higher mounting position for the engine. But that is not an option since it would take time and change the original design of the boat.

So there is only one solution (yes, scrapping the boat was suggested by friends) and that is to build a jack plate that is firmly attached to the transom and provides a higher mounting position for the engine. A quick and easy way one might think.

However there is a condition to this small boat project: the budget is just about USD $0. All parts used to rebuild it have to come from spare parts or scrap or anything else found, given or stolen from friends and neighbours. The challenge is to keep this boat running using spare parts and scrap for as long as possible.


1 pcs. ~70 years old plastic boat

1 pcs. ~35 years old 25 hp long shaft Mercury outboard engine

Lots of friends at different places, i.e. at a car scrapyard, a construction company, etc.

Scrap and spareparts wherever we can find them

Time and an endless stream of (mostly stupid) ideas

No budget

Step 1: Identify the Problem

One is constantly learing. I had no idea what the difference between a short and long shaft meant until I tried to use a long shaft engine on a boat constructed for short shaft. Performance is reduced, fuel consumption increases and the boat can actually flip over if turning too hard. The long shaft puts the propeller too far down under the boat.

So this engine has to come up. And also because the powerhead gets flooded when decelerating hard, especially with four people onboard.

Step 2: Measure, Measure, Measure

To form a plan one has to know the circumstances of the solution. In this case: where are we and where do we need to be? Careful measuring shows that the desired position is actually in line with the boat's deck, so this sets our goal.

Step 3: Beg Steal or Borrow

So here comes the next problem: How to build some kind of jack plate and how sturdy does it have to be? From what material? Stainless steel? Heavy and expensive. Wood? Welll... wood and water is not a perfect combination for a lazy man. Aluminium? Sure! If you can find someone who has the right dimensions and can weld.

Fortunately it does not have to be that hard. A combination of aluminium and plywood is more than enough, at least for this 25 hp engine. A friend had a piece of scrap aluminium U-bar and another had some thick plywood hanging around I could get. The plan is to glue together enough pieces of plywood to fill out the aluminium U and then bolt the U-bars on to the transom so that the plywood block fits between.

Step 4: Time for Assembly

Yes, the transom would have looked great with some fresh paint and TLC. But not this year, the boat has to go into water before the season ends.

Measurements were almost ok and the end result is functional: a place to hang a long shaft outboard engine on a boat constructed for short shaft.

Step 5: Getting There!

Of course there are unforeseen circumstances. Like for example that the plywood block is too thick and has to be slimmed for the engine grip to be able to grasp it. This is common when one builds from free or or from re-purposed material, you just have to make the best of what you have.

Anyway, the engine is once more on the boat and the new steering arrangement is almost perfect, just some small adjustments and it does not interfere with the plywood or aluminium.

Step 6: All Done

Does it not look great? For a version 1.0 it is not bad at all. The wooden parts were treated several times with linseed oil so that they should last a couple of years. They are not much exposed to water, of course they get splashed, but are not constantly in the water. And the boat only sees fresh water lakes, no saltwater.

Next year's project will be to deassemble everything again, redo the transom with more reinforcements and paint it nicely before reassemble.

Step 7: Time to Enjoy

What is there left to say? It is a hit, mission accomplished! The boat does 23 knots with two full grown (ehrm...) adults, is stable and handles great.

Total cost of parts is about zero, only some stainless bolts and nuts + glue and other consumables. Which of course does not come for free but is nothing considering that boats are black holes in the water where you throw your money into...

Those with sharp eyes and some knowledge of outboard engines might have noticed that the steering cable arrangement was redone while we were at it, from a left-right movement to a fore-aft movement. This was because of a 90 degree bend that the steering cable did not like and which made steering very heavy. We had to move the position of the steering arm on the engine 90 degrees clockwise and create a new steering bracket. It works great but that is a story for an other article...

Plywood Challenge

Participated in the
Plywood Challenge