Boating Advice: Trimming your boat (Part 1)

All modern power trailerboats benefit from the correct use of power trim and careful weight distribution. Learning how to trim your boat properly is not difficult, but it will take practice. Let’s get back-to-basics in part one of this two-part feature article.

OVERVIEW
- Sharpen up – learn how to trim your boat
On waterways right around Australia, on any given weekend, you will see dozens of boats running along with their bows either pointing skywards, or ploughing through the water and pushing up heaps of spray.

These are badly trimmed boats. More often than not, the skippers of these boats have no idea their boats are trimmed badly and handling poorly.

When running in relatively calm, enclosed harbour waters, poor boat trim and weight distribution may not have severe consequences (although the resulting wash can).

However, in offshore waters, where you have to deal with bigger seas, you can quickly get into trouble with a badly trimmed boat.

For this reason, and to simply improve the handling and ride of your boat, it is important to learn how to load and trim your boat. Let’s tackle the loading issue first.

Do run through the 10 photos each including a caption accompanying this article to help explain the variables, causes and effect, of boat trim.

WEIGHT DISTRIBUTION
- Spread your load evenly
Before even moving away from the launch ramp, experienced boaters will automatically check that everything onboard is stowed correctly, and that the boat is sitting evenly in the water.

Loose items should be tied down or stowed in lockers where they can’t move. Heavy items like tackle boxes, big ice boxes filled with drink, etc, should be positioned evenly around the boat.

Essentially it all comes down to ensuring that all of the weight carried in the boat is distributed evenly. The boat should not list to one side because this will be amplified once the boat rises up onto the plane.

On a fore-and-aft basis, most experts would agree that you should place slightly more weight in the stern of the boat, rather than up the front.

Having heavy items stowed in the cabin or under the windscreen in runabouts can make the boat difficult to trim up — and may cause it to plough through the water. Of course, every boat is different. Some experimentation will be required to get your boat set up perfectly.

On those occasions when you are taking family or friends out boating with you, make sure you assert your authority as the captain of the boat. Remember: the skipper is responsible for the people onboard and everything that happens during the trip.

With people you don’t know too well, you may feel a little awkward ordering them about on the boat, but it has to be done. If you find there are three people sitting over on one side of the boat, and it is listing severely, don’t just ignore it. Ask them to move to a different seating position so that the boat remains evenly balanced.

COUNTERING THE HEELING EFFECT
- Adjust the running angle of your boat
Once you move away from the launch ramp and accelerate from a displacement speed, up on to the plane, the handling characteristics of your boat will change.

You will notice that moving weight around the boat will have a magnified effect. You will also find that the sea and weather conditions will influence the way your boat handles and rides across the water.

For example, when running side on, or beam to a strong wind, you may find your boat will list or heel over into the wind. This is most common on large cabin boats, or those with high topsides, enclosed canopies, etc.

Counteracting this 'heeling' effect in single engine craft relies on shifting weight to the other side of the boat. A better alternative is to fit the boat with trim tabs. More about trim tabs later on.

Why is this even necessary? Well, to get the best out of a planing hull, to ensure that it handles and rides safely, economically, and comfortably, you need to trim the bow of the boat up or down to suit the specific conditions. Wind, wave chop, ocean swells, current — all of these things influence how your boat handles and performs.

For example, when running downwind, or before the sea, most boats should have their bow trimmed well up and the weight inside the boat distributed toward the stern. When running down the waves, you can imagine that your boat’s natural inclination is for the bow to plunge down into a wave trough. Being able to raise the bow up helps keep the bow clear of the water and should prevent it from burying or, worse, “broaching”.

Broaching is a term used to describe what happens when a boat runs down the face of a wave, digs into the trough at the bottom, and then slews sideways. If you have ever watched a surf boat race you might recall seeing a broaching situation. The surf boat slews sideways at the bottom of a wave, capsizes, and throws the crew overboard. Given big enough seas - like you might encounter when crossing a bar - most trailerboats will capsize in a similar situation.

In rough seas, there is much you can do to avoid a potential broaching situation. Shifting the weight in the boat aft, trimming the boat up, and driving the boat so that it stays running or sitting on the back of a wave (instead of running down it) will all help.

Learning how to trim your boat properly is not overly complicated, but it does take practice.

(ED: Of course, not all boats perform the same, and some can have a tendency to broach irrespective of your trim input. Some designs with a very sharp entry that run smoothly into a headsea might not be as forgiving running back downsea, even when trimmed out and in calm conditions, especially with maximum horsepower adding to the effect.

So it's important that the boat is set-up right from the beginning, too, that engine heights are right and the boat isn't driving its bow in too deep when there is no trim applied or the boat is running in a neutral trim position.

Thankfully, today, we now rarely have a situation where a new boat and motor isn't properly paired, thanks to factory-rigging, pre-testing before market release, the proven boat/motor/trailer or BMT production rig being water tested before you buy it, and the fact those dealers remaining in the marine industry are surviving on their reputation for getting these very things right.

But it wasn't always this way and buying second-hand rigs certainly exposes you to a great range of possibilities in respect of performance. Tip: New boaters would do well to put their faith in a factory-rolled BMT rig with proven, predictable performance.)

Next Week: In the conclusion of this two part series we will examine how to adjust your boat trim for best performance and economy. We will also reveal how to fine-tune boat trim with dual engines and trim tabs.

Meantime, some of the big marine engine makers are getting pro-active with tackling the issue of trim and creating automatic boat levelling systems. Check out Mercury's Active Trim.

PIC 1
For good balance and trim in small craft it is very important to spread the weight of passengers and gear evenly throughout the boat.

PIC 2
Small side console boats will naturally heel to starboard with just the skipper onboard - so you may need to compensate by moving gear and tackle to the other side of the boat when fishing single-handed.

PIC 3
Manual start, tiller-steer engines do not have power trim, but you can still adjust the running trim angle via a steel pin that moves into different slots on the engine-mounting bracket. The trim angle is set poorly here, as the angle of the engine is driving the bow of the boat up into the air making it difficult for the boat to plane.

PIC 4
This is much better. The outboard drive leg has been lowered a pin slot (or two) so that the thrust of the engine is now lifting the stern up, and driving the bow down. This helps the boat to rise onto the plane and to run faster, more economically. With a load of two people onboard this Quintrex Wanderer is now nicely trimmed.

PIC 5
In a following sea - or when coming in through a bar - trimming the engine and the bow up (positive trim) will help to prevent the boat from broaching.

PIC 6
The skipper of this Snyper runabout is running with some negative (down)?engine trim for the trip out through the bar. This helps to keep the bow down and stop the boat from leaping off waves.

PIC 7
At first glance this Mako looks to be trimmed with the bow too high out of the water, but in calm conditions, trimming the boat out like this provides a faster top speed and maximum fuel economy - due to reduced drag.

PIC 8
A Stacer 579 Crossfire trimmed for speed and economy in flat water. Note how the forward passenger is sitting over on the port side to offset the weight of the skipper to starboard - balancing the boat nicely.

PIC 9
High sided, ultra-deep vee craft like this TMA 25 will tend to heel into a cross breeze underway. Fortunately this lean angle is easily corrected with trim tabs, which is why we recommend fitting them to all single engine craft over 6.0m in length.

PIC 10
Heading out through the Gold Coast Seaway, the skipper of this Quintrex Yellowfin has dialled in a lot of negative engine trim to keep the bow down. A bow down running angle presents the sharp hull forefoot to any incoming chop, which should soften the ride.