Here is a bit from my experience on the issue of outboard performance addressing some of the most common issues brought-up on the board:
The 'Mephisto Cat' is a 'Well in the lazarette' / outboard model' from the factory.I am happy to not have to deal with an oily bilge! Although I could learn a thing or two about diesels... And I salivate a the big & handy storage space that is available in the lazarette to those of you with inboards... Hmmm...
I can only dream of the day when a nicely suited electric motor is available!
In any case; So far I've used a 2003 NISSAN 6HP, 4-stroke outboard engine with the long shaft (20”) on the Mephisto Cat. This NISSAN model, as well as some other brands (Mercury?), is apparently made by TOHATSU so they share the same mechanicals - only the marketing bits are different...
I’ve used this motor for a handful of seasons in San Francisco Bay, as well as at Marina del Rey (Santa Monica), and on coastal voyages from Ensenada, MX, to San Francisco as described in previous posts on the Mephisto Cat gallery thread: http://www.pearsonariel.org/discussi...ead.php?t=1552
The typical issues faced with outboards on Ariels & Commanders seem to be the following:
1.- Will the motor fit in the outboard well?
The 6 HP Nissan fits quite nicely in the well being able to rotate pretty much throughout its full range. The lazarette cover closes, clearing the top of the motor by two to three inches. (I am unsure if the internal tank version of this motor would fit as the internal fuel tank cap is located at the top of the motor cover, and sticks out at least a couple of inches...)
The bottom unit is thin & slender (unlike some other brand's models) allowing for an easy fit in the well (there are maybe 3" inches to spare around the widest part of the lower unit as you lower it thought the well...) The slenderness of the bottom unit also helps in reducing hydrodynamic resistance while sailing with the motor in the motor well – which I often do….
This motor only weighs 55lbs (Per Nissan) which makes it easier to handle. I think that this is the heaviest you can go while still being able to (relatively) easily handle an oddly shaped mass as an outboard motor - especially at the point where you are lowering it into / pulling out of the lazarette.
2.- How much power do you need to power an Ariel / Commander (HP)?
I find that this motor moves the boat quite well. It will cruise at about 4 to 4.5 knots at ¾ throttle, and will reach hull-speed (~6kt) at a bit less than full throttle.
While sailing in SF bay in the past, where the winds and currents are not to be ignored, I have found the need to use the full power of this motor while fighting a strong current, or while motoring into a channel with a strong wind on the nose.
While using the motor during coastal cruising, I found that when faced with strong winds on the nose - and the resulting long-reach wind swell - the going gets slow... Mostly because out in the open, the wind swells easily kill your forward momentum.
In these cases a bit more horsepower might help, but these are unusual circumstances for these boats. AND I would argue that if you find yourself in this situation at that point you’d be MUCH better off sailing-off with a reefed main and a storm headsail as this will improve your ride and likely progress as well, so the benefit of a bigger outboard in these cases may never be enjoyed… while you’d ALWAYS be burdened by the big outboard’s weight. **
However, in my time spent in coastal marinas, such as Marina del Rey / Santa Monica Bay where currents are negligible, I found myself wishing for a little (maybe 2-3 HP at most) two stroke motor that I could pull out in a jiffy… This would be more than enough to get in and out of the marina when the winds were blowing. If I were still in this environment, I’d definitely go with the tiny motor. If you are in a lake environment doing mostly daysailing, I'd really consider this route...
** As I've learned more about this issue, I found that the ideal solution in this case (from a hydrodynamic standpoint) is not really more horsepower, but rather a larger prop diameter at a lower pitch to increase efficiency of the available force... Providing what is known as increased 'bollard pull' -the equivalent of more torque in a car engine- with the same horsepower...
Unfortunately, these motors will not physically acommodate a prop much bigger than what comes from the factory...
3.- How fast will the boat go?
6HP will get you to hull speed in most conditions. There is no need for more horsepower. - 20HP will maybe give you hull speed PLUS maybe 1 or 2 knots more, PLUS a big bow wave in front of your boat… and this while using MUCH MORE Fuel. In short, there is no need… (unless, as I described above, you will be ONLY sailing against very strong winds in sheltered waters -with no wind swell. These conditions would allow you to enjoy the extra horsepower to fight the wind, but these conditions are unlikely…)
4.- Shaft length
My motor has the 20” long shaft. (Note: For 2009, Nissan is offering a 25” extra-long shaft.)
I found that the 20” long shaft works really well on these boats. The steepest swells faced were while motor sailing around Point Conception where we saw 8-10 ft ocean swells that were far apart enough to not present a problem (11-14 seconds). Big swells are not a problem for the motor, but when these swells are reflected by the concave coast between Point Conception and Point Arguello, and become 4-5 ft swells coming in opposing directions, plus toss in a 1-2 ft wind swell… All of these combining at random can present a tall chop which can be a challenge mostly for your comfort.
Even in these conditions the prop managed to stay in the water but did suck in some surface air for an instant a couple of times as the conditions above combined to produce a steep/deep chop. Note that when the cavitation happened, it was quire unexpected based on the behavior of the boat at the time, and never due to a severe pitch or roll - the prop seems to stay in the water while pitching /rolling. What seemed to do it was simply a very tall / steep chop, in my case, resulting from a combined wave/swell.
The cavitation was only for an instant causing the revs to increase, but only for an instant. I do not think that the motor had time to reach max revs. I do not think that cavitation is an issue for the 20" shaft lenght based on the amount of time that the motor had to work in these conditions...
In short; If I were in the market for a motor, I'd stick with the 20" version...
The 25” shaft would provide a bit more of a margin against the above situation, but most of us would not be in this stuff as a matter of routine… (hopefully!!). The down side of this extra length would be a bit of additional drag while sailing, a small bit of added weight, and the 5 extra inches increasing the required storage space.
Thoughts?
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