Range of C-Dory at Hull Speed

[MikeMac]

Jim,
The Honda prop tables for a 50 on a 22 cruiser show 13.3 MPG at 4 MPH at 1500 RPM, and 7.5 MPG at 6 MPH at 2000 RPM. Yikes, quite a drop! Phil Bolger wrote somewhere that 6 is the magical psychological number to make you think you're actually getting somwhere so the C-Dory seems likely a poor choice for a displacement boat. But that's with a 50. I'd love to know what would happen with a 15 or 25 which would be more in line with the engine sizes on the Nimbles.

If you had to get to Mexico, slower is better!

Mike

[thataway]

Not that a C Dory is a poor choice for a displacement boat, but that the length water line of a 22' C Dory is short, and the more effecient speed is the one which is close to sq root of LWL--or even 1.2 x sq rt LWL.

Could you make a more effecient hull? Certainly--for example I have a friend who made a wave piercing cat, which is 32 feet long, and weighs 1200 lbs, all up, including a 15 hp outboard. The 15 hp engine will push that boat at 12 knots--at a gallon an hour. A very effecient boat and hull--but a very light boat, and very limited accomidations--enough room for a sleeping bag on the floor of the cabin, a camp stove in the cockpit for a stove and a couple of gallons of water. If you increase the weight, the effeciency will decrease.

Or you could make a very narrow C Dory, but it would be much less stable, have less accomidation and probably would not do that much better MPG. Back to all boats are compromises.

The engine smaller than the 50 hp, may do 10 to 15% better, but that is all you can expect. For at boat this size, it is as about effecient you can get with the accomidations which it has. There are some sailboat type hulls which might be slightly more effecient, but again only in the 10 to 15% better effeciency. Could you take a C Dory 22 down the Pacific coast of Baja?--yes, you could--there are enough places to pick up fuel if you had a range of 300 miles. But what about comming back up the coast? You would be most likely pushing into wind and waves which would be most uncomfortable--and would decrease the range, perhaps to the point of marginal range.

We averaged over 150 miles a day when sailing--or about 6 knots. If you are averaging 4 knots, then 100 miles a day (24 hour day). Some small sailboats only do this speed. On our West bound Atlantic crossing we made about 170 miles a day--At the same time a 24 foot sailboat made under a 100 miles a day--he took 30 days, and we took about 17 days. Not sure how that relates to "going anywhere"--both boats crossed the Atlantic safely. I would not consult Phil Bolinger on passage making--he has designed multiple small boats, often of unique design and written both books and magazine articles on his concepts of simplistic design. But how many passages has he made? The point is, that speed is very relative. We have met one man who was very happy pushing his 28 foot garvey type house boat to Sitka AK up the inland passage at about 3 knots average. with an 8 hp outboard. Others want to go 25 knots all of the time....

[RJD Wannabe]

These #'s make the idea of trolling slowly back home very attractive. A big spread can cover some territory trolling, doubt if the increased drag would make a huge difference. 10mpg on the way back would be impressive.

[thataway]

Incidently when cruising we had a minum speed under sail, we started the engine--and that was averaging less than 3 knots over an hour's peroid of time. When racing, of course there was no minimum speed. We have anchored to keep from going backward in currents, and drifted for a day in the middle of the Pacific on the way to Hawaii...

[smittypaddler]

On my great loop trip I averaged 3.75 mpg over 7000 miles, but one day I traveled on one engine at a time, with the other engine off and out of the water (I have twin Honda 40s on my CD22), at about 6 knots. I got between 6 and 7 mpg over a distance of about 50 miles on that day. With twin 20-gallon tanks that gives me a range of about 240 miles.

[iggy]

Minor digression to Dr. Bob:

Isn't it aggravating in a 'race' when you have to put out your anchor to avoid going backwards? A close second is using a July 4 punk to create the slightest wisp of smoke because there is not nearly enough wind to move the tell-tales. And of course, most aggravating is watching your competition that happened to go inside (if you went out), or out (if you went in) getting wind before you do, while you and all nearby boats continue to drift. On overnight races in Puget Sound years ago there would always be a great thrill trying to locate your competition with binoculars in the wee-est early hours of dawn, especially if you have been essentially drifting most of the night.

iggy

[thataway]

Yep, Iggy. Once after a 200 mile race, I was in sight of the finish line, and a boat which had to give me a lot of time, was just able to squeek across the finish line before the wind died and the tide turned. The boats which didn't anchor, were swept about 15 miles out to see on the tidal flow. We finished about 8 hours later--no wind, but mostly the early tide flow pushed us across the line....

I always contended that many long distance races are won at night--when most folks back off and don't pay as much attention to the wind and sea conditions...

Regards,