Not all powerboats perform as well as they should, yet fixing the problem is often surprisingly easy
Those who buy a new powerboat from a reputable dealer or manufacturer usually do not have a problem. The engine will have been set up correctly, buyers will have been offered a choice of propellers and perhaps even a discussion about trim tabs (although some manufacturers are still surprisingly precious about this).
However, those who buy secondhand may not be so fortunate. With a number of secondhand boats behind sold online with no intermediary (such as a dealer) between buyer and seller, it is truly a case of caveat emptor (buyer beware).
While there are many good secondhand boats around, especially those of recent vintage, there are also those that have been something of a test bed for their owners.
These are the owners who like to potter, have a project and see if they can get "another knot or two out of the old girl" with a bit of tinkering.
Some of these are, of course, wonderfully inventive chaps and our reputation for Kiwi ingenuity wouldn't exist if it wasn't for their successes. However, not all who tinker are so gifted.
So, what does one do if one finds their boat is not performing as well as it should? Generally speaking, there are three areas where things can go wrong: the way the engine is set up, in particular its height on the transom; the size, pitch and type of propeller being used and the way the boat is trimmed.
According to long-time Propeller magazine writer and former offshore powerboat racer Barry Tyler, the first place to start is with the propeller.
If everything is properly set up, an outboard, or an inboard, should be able to reach its maximum rpm. If it doesn't, it could be that the size or the pitch of the propeller is wrong.
So if the engine is only revving to 5500rpm instead of 5800, the propeller could need to come back an inch or two in pitch.
The best way to sort this problem is to talk with an experienced outboard mechanic (every reputable dealer has a least one on staff).
Getting it right is not just a case of gaining another couple of knots at the top end, either. A properly pitched propeller could also mean reaching your cruising speed at lower revs, meaning lower fuel consumption.
Other options include longer-lasting stainless steel propellers (most "standard" props are aluminium), "sports" propellers and various types of performance propellers aimed at those keen on high-level water sports or racing.
Once the correct propeller has been found, attention generally turns to the way the engine is set up.
"The whole point of the set-up exercise is to find the optimum 'sweet spot' where the balance of the boat is right, the ride is at its most efficient and maximum power is being transferred to the water," says Tyler.
The height of the engine is crucial. Too low and there is a loss of efficiency; too high and there is the danger of cavitation.
According to Tyler, a good rule of thumb is for the cavitation plate of the engine (when level) to be at the same level as the keel line of the boat. If it is too low, it can sometimes be raised on a DIY basis, depending on the size of the engine, the number of mates available to help and the availability of a suitable overhead structure (such as a strong tree branch) from which to hang the motor.
Doing this yourself can be relatively easy but also fraught with problems, depending on what equipment and tools are available, the state of the engine and the transom and the competence of the DIYer.
The other major area where boats underperform is in the way they are trimmed. As Tyler points out, trim is basically another word for balance and it doesn't take a lot of imagination to realise that a well-balanced boat is going to perform a lot better than a poorly balanced one.
There are two types of trim and both are equally important. Fore and aft trim in an outboard-power boat, providing the engine is big enough, is usually controlled by the angle of the motor against the transom.
If the outboard is trimmed in or "down" it is tucked in flush with the transom or even slightly under it. This "flattens the boat, bringing the bow down. In most cases, engines are only trimmed in when transferring from an at-rest position to coming onto the plane.
Once on the plane, the engine should be trimmed out until the sweet spot is found.
This is when the boat is at its most comfortable and its most efficient. It is also usually when the water is breaking about a third of the way from the transom.
The weight on the wheel can also be a good indication of where the sweet spot is: if the wheel wants to pull to port, the engine is still too far in; if it pulls to starboard, the trim is too high.
Side-to-side trim can be equally easy to fix. There are normally two causes of a boat leaning over instead of sitting on its keel: either it is being affected by the wind or the weight on board is not evenly distributed.
In the latter case, it can be a simple matter of moving bodies, fuel tanks, dive bottles and the like to the "up" side until the boat returns to level.
This will also work in the case of windage but only if there is moveable weight on board.
Despite opinion to the contrary, a power boat leaning over in the wind is not caused by bad design. It is a result of the wind hitting the bow and blowing the boat off course.
As skippers we are not going to put up with this, so we turn the wheel in the direction of the wind to bring us back where we want to go.
When we do this, the boat leans over (as it always does when we turn the wheel ) - unless we are in a multihull, of course. The best and easiest way to fix this is to fit trim tabs. They are widely available, relatively inexpensive and, if properly fitted, generally work very well.
Fixing set-up problems
Check: Propeller, engine set-up, trim
Get advice: from outboard mechanics at marine dealerships
See Barry Tyler's feature: Getting Your Ride Right in the August/September issue of Propeller magazine and also online at www.propellermagazine.co.nz.
