Before proceeding to mounting a bracket on our transom we should first assess whether it is compatible with our boat and, of course, we need to know what we want to gain with this addition and to what extent. Therefore we must weigh the consequences and decide which the intended use of our boat is.
Does the use of a bracket improve the performance of every boat? And if so, what would the appropriate length be?
The answer is of course negative: whether the mounting of a bracket will improve the performance of our boat mainly depends on the center of gravity/buoyancy balance, the type of the hull, the engine or the engines we are going to mount and, of course, on the intended use of our boat.
We need to know that the installation of a bracket results in a backward shift of our boat's center of gravity. The extent of the backward shift of the center of gravity will depend on the length and the weight of the bracket and on the weight of the mounted engine or engines. But is this shift tolerable by our boat, is it needed or is it required in order to be able to effectively use our boat? If none of the above is true, then the backward shift of the center of gravity can have negative effects on navigation, particularly when mounting one or two four-stroke engines with XL lower units.
There are types of hulls, including stepped hulls, where weighing of the boat is so "strict" that no change is accepted and the mounting of a bracket would only result in negative effects on the operation of steps. The philosophy of the stepped hulls is based on the "coincidence" of the center of gravity and the center of buoyancy and if this balance is compromised there will be afflictive consequences on the navigation of the boat.
There are boats that have their bow high by nature, and in these boats, the backward shift of the center of gravity would lead to even higher bow lift with unpleasant effects on navigation.
On the other hand there are boats which keep their bow very low and a backward shift of the center of gravity would only induce beneficial effects.
Of course, there are instances where the hulls have design defects or the boats are not properly weighed owing to structural defects, and these are the cases where the use of a bracket is imposed in order for the above defects to be corrected.
However, we should not do injustice to some boat manufacturers who have foreseen in advance the application of a bracket and so they "construct" their boats accordingly.
It is understood that before we decide to mount a bracket, we need to be sure if this matches to our boat and its use as well as if its center of gravity allows it. At the same time, we must consider what the length should be depending on the extent of the backward shift of the center of gravity we want to achieve on our boat.
Let's look at the benefits a properly mounted bracket offers:
- First of all, the mounting of our engine further back on the bracket make the stern heavier and automatically the bow tends to rise up (as we have emphasized above, the elevation of the bow is an advantage only to the boats which keep their bow too low at standstill or during cruising) . This means that we are now able to lift the bow much higher when we trim up the engine. The response to the trimming is greatly improved.
- We can mount our engine higher on the bracket than on the transom as the water flowing out from the bottom of the transom is rising up. This means that the hydrodynamic drag of the engine lower unit is reduced, as the immersed area is smaller. Furthermore, the load on the engine is reduced and so the engine can increase its rpm, which enables us to switch to a higher pitch propeller.
- Our propeller is less submerged in the water when running - after we have mounted the engine higher - as well as in freer water flow compared to the water flow observed immediately behind the transom that is more turbulent. This, among other things (better "bite" in "cleaner" water etc.), means that we can match a more efficient propeller that is designed to run close to the sea surface.
All the three factors above –i.e. less wet hull surface, less gear case in the water and less drag of the propeller itself which increases its efficiency as it operates in "cleaner" water - result in an increase of the top speed of our boat and improve the overall fuel consumption.
Apart from improving the boat's performance, the mounting of a bracket provides us with:
- More free space inside the boat, which gives us the opportunity to exploit it according to our needs, for example to design a comfortable and large aft sundeck.
- More free space around the engine, which will be very useful for our bath, swimming, diving, fishing or even when we need to do some work on it.
- Increased distance between the engine and the cockpit, which in turn results in minimizing its noise. This is particularly important in long trips, as it allows us to enjoy the beautiful wind and sea sounds.