Improving the Performace of your Outfit
Unable to get afloat because of constant bad weather during what was supposedly the summer, we eventually found ourselves having to put the boat in at Knott End as the only place we could think of to do a few hours of meaningful propeller testing on behalf of Suzuki and Warrior Boats. Our brief was to find the most appropriate prop to get the best out of our fully laden Warrior 170 fitted with a Suzuki DF90 engine, information that could very likely be of use to the owners of other heavy V-hulled boats of similar weight. The problem was that when we did the original on-water press day testing of this outfit down at Weymouth, it was just myself and Charlie onboard. Dave was away somewhere, and the boat itself had nothing else in it other than a single tank of fuel and the cameras. So it was always going to give its best in terms of rpm and mph performance. What boat wouldn't. It's when you fill it up with batteries, anchors, extra fuel, and lots of heavy fishing tackle, plus in our case an additional 17 stones of angler in the form of Dave that you start to get a clearer picture of just how it will really perform and handle. At Weymouth it was clearing 6000 rpm and 40 mph without any problem, and with the trim tabs fitted to the fisherman model, though not the leisure version which was also available for a blast around the bay under identical conditions, it felt like the best balance, ride and pace of any trailed boat I had hitherto fished from. Even back at home it still felt good. It wasn't until we got one of those all too rare flat calm days when we could really open it up that we noticed just how much the rpm and mph had dropped. What's more, the difference seemed out of all proportion to the extra work now being asked of it. Then I remembered an exchange of emails with Suzuki sales and marketing manager Gareth Lumsdaine who had hinted that possibly the prop the engine came fitted with as standard might not be the best option for the Warrior 170, hence these trials.
Wanting to help us get the performance of the boat absolutely right, Gareth arranged to have a couple of other suitable 'likely candidate props' sent out, which along with a suitable set of tools made the journey with us Knott End. Just as we got there, a Predator 165 was coming in forced back by the wild sea conditions at Wyre Light. Seeing that we were about to launch, and wondering if we could make any use of their bait, they started asking what we had planned, so we told them. They then told us how we should be getting much more out of the DF90 as they could get 50 knots out of their Predator with a 60 on the back, which isn't bad going as the Predator website quotes the 165 model with a 60 hp on the back as delivering a very creditable 37 mph when empty during a Sea Angler Magazine boat test. This makes wonder just how many people do actually know how fast, or more to the point in cases like this, how 'slow' their boats are going. It isn't a big job to check it out with the GPS speed over ground facility. Or perhaps exaggeration is an inherent must have quality to become an angler. But to be honest, to get the best out of any outfit in terms of assessing the potential need for expensive trim tabs, prop changes, or even something more down to earth such as buying more petrol than you might otherwise like, having some idea of your engines optimum rpm requirement, its fuel consumption, and its potential as well as actual speed is a must. We hadn't checked out our fuel consumption, though we had done similar trials with aevious 4-stroke outboard , which gave more than half as much again as its predecessor 2-stroke. That said, in the interests of fairness, it has to be said that the Evinrude E-Tec is a 2-stroke that is fully compliant with current EU emissions standards, and is said to be at least as economical as a 4-stroke. But not necessarily all 4-strokes, as there is something of a technological push on just at the moment to improve fuel economy, with Suzuki's new DF range (2009) claiming as much as 22% improvement over previous similarly sized Suzuki models.
The original prop that came with the engine was 14 inches in diameter with a 19 inch pitch (the distance forward the propeller will have travelled through one complete revolution- in this case 19 inches). So at face value you might think that the greater the pitch, the faster the boat will reach it's destination, and consequently, the more efficient it will be. At the same rpm that would be the case. But can the rpm be kept at the same rate. It's rather like a car trying to struggle up a hill in top gear – it can't always be done. Petrol entering the bores of an outboard engine might not necessarily all get burnt because of the loading, wasting fuel and loosing power. It is also possible through inappropriate pitch to get more rpm yet not get more speed, and loose out through fuel wastage into the bargain. So getting it right is something of a balancing act, which in our case, as with most small boating situations, can only be resolved through trial and error. So where do you start. Well, having had the 19 inch pitch on for several months already, and being well aware of the situation, we already had data for that prop which was down to just over 5000 rpm and around 30 mph. So we decided to do the first prop change on the driveway at home to minimise messing about in the water. We chose to fit the 17 inch pitch first because we thought that the 15 inch would be too much in terms of additional load. That just gave us the 6000 rpm we had been looking for and upped the flat out speed to 33 mph. Then we took the boat in onto the ferry beach to fit the 15 inch pitch, the results of which took us completely by surprise by going over 6000 rpm with a top speed of almost 36 mph. The question then was, what were the implications in terms of the life of the engine, and also how might this affect fuel consumption.
That information was passed back both to Warrior and to Suzuki for their input and suggestions as to which of the new pair we ought to go with, as both achieved an rpm within the optimum range. The couple of extra mph for use on those rare occasions when you can actually open the throttle wide is neither here nor there if there are other, more relevant considerations. The general feedback consensus seems to be to stick with the 15 inch pitch. And while I was over at at Warrior talking to Phil and Paul about it, Phil showed me a performance bulletin put out by Honda for their new BF60A model. This relates rpm to speed and fuel consumption done using a Warrior 165 fitted with GPS, a rev counter, and a digital fuel flow gauge, and while it will not be exactly the same for other makes or models of outboards, or for other boats and loadings, what it does do is demonstrate trends of engine performance with fuel consumption. Take a look for yourself. Things like the jump in fuel consumption of 3.6 litres per hour between 5500 and 5800 rpm to achieve just 1.7 mph more doesn't bear thinking about. You wouldn't notice 1.7 mph on an empty featureless sea. But considering that 4.5 litres is a gallon, then 3.6 litres to get that extra 1.7 mph would be a massive difference to the contents of your fuel tank. What the table also shows is that once that engine gets above say 4500 rpm fuel consumption generally starts to rocket while increases in speed up much more slowly.
HONDA BF60A LRTU PERFORMANCE DATA BULLETIN No. 002
| RPM | Knots | Litres/Hour | Miles/Litre |
| 850 | 3.0 | - | 3.24 |
| 1000 | 3.3 | - | 3.08 |
| 1500 | 4.8 | 1.8 | 2.48 |
| 2000 | 5.2 | 2.3 | 2.21 |
| 2500 | 6.4 | 3.3 | 1.94 |
| 3000 | 8.7 | 4.7 | 1.84 |
| 3500 | 12.6 | 6.3 | 2.00 |
| 4000 | 17.1 | 7.3 | 2.32 |
| 4500 | 21.4 | 9.4 | 2.27 |
| 5000 | 24.2 | 13.3 | 1.84 |
| 5500 | 26.5 | 17.1 | 1.57 |
| 5800 | 28.2 | 20.7 | 1.35 |
| 6100 | 30.7 | 21.7 | 1.40 |
Performance in terms of acceleration, top speed, fuel consumption, and also ride can be improved in ways other than changing the engines prop. When done in conjunction with it, then so much the better. Getting the best out of an engine, and therefore the boat it is pushing along can be had by something as simple as getting the engine trim right. There is no hard and fast formula for this. Because of loading, and varying sea conditions, every situation will be different, and likely even to change on a trip by trip basis, or even during a trip. A case then of playing with the trim button on the throttle and feeling for the difference. It is as simple as that. Or at least it can be, if the transom of the boat allows the engine trim sufficient range of adjustment, which unfortunately isn't always going to be the case. It's all down to transom angle. When an engine is tilted up away from the transom it pushes the back of the boat down and the nose of the boat up. The reverse is true when the engine is tilted the other way. Because of the weight of things like batteries, anchors and fuel, all of which tend to be stowed at the very back of most boats, plus the weight of the engine itself out at the furthest extremity of the boat, not unexpectedly when any measure of power is applied, the bow of most boats comes up. This causes the boat to start porpoising, which is uncomfortable, uneconomical, inefficient, and in extreme cases, even dangerous. Getting the engine to go down further would help solve the problem. But where the transom angle won't allow this you will have to resort to other measures. The most common of these, and certainly the cheapest, providing it is done at the time of engine fitting is a plastic transom wedge. This will give the engine a bit of extra reach, which might turn out to be enough. If it isn't, you might want or even need to consider fitting a Doel Fin or trim tabs which are discussed in the article Trim Tans under the menu sub heading of Product Reviews.
FOOTNOTE: Sven Hille who fishes out of Rostock in northern Germany where he trolls the Baltic for Salmon and Sea Trout from a Warrior 165 came up with some interesting performance information. Using an older model Suzuki DF50, he clocked up the best part of 300 hours motoring in less than two years. Not only that, he also kept a very good data set in terms of hours worked, engine loadings and fuel used. Then in November 2009, Sven bought a new Warrior 165, this time with one of the new more fuel efficient Suzuki DF70's fitted, and found that while he had 20 hp more than before, at around 4000 rpm (20 knots) he was actually using 25% less fuel, which goes to show that Suzuki's fuel efficiency saving claims of up to 22% for the new DF models compared to the old range are actually being borne out.