This bulletin board, hosted by the CDSOA, Inc., is the on-line meeting place for all Cape Dory owners and groups. We welcome everyone's questions, answers and comments about Cape Dory sailboat
drysuit2 wrote:With any power: you need to be moving in order to steer. That is change direction...
Inboards are efficient going forward, and add ballast down low where you want it. Buy they suffer from prop walk and perform poorly in reverse.
Technically speaking, water must move over the rudder to change direction but the boat can be standing still. A good blast of "forward" can kick the stern quite a bit.
Help me with the physics of prop walk. Why would an inboard "walk" and an outboard not?
Because you can change the angle of attack on an outboard to compensate. Whereas an inboard has a fixed prop. When backing up with an outboard, I will often steer with the outboard and the tiller.
However, if you leave your outboard in a fixed position, you will still have some prop walk. But not as much as if the prop is forward of the rudder.
This thread has gone way off track. Mr. Gregory welcome to the world of Cape Dory’s. They are wonderful forgiving boats. You will have many years of enjoyment from yours. [No matter how you rig your auxiliary engine.]
WaywardWind, it sounds to me like you really need to go sailing. If you would like, you are invited to come sailing with me this weekend. You are always welcome. Consider it an open invitation.
I will never understand physics the way you do. All of my knowledge comes from 40+ years of sailing, and 15+ years of running an ASA certified sailing school. So most of my knowledge is empirical: based on my experience sailing many different types of sailboats over the years; and the simple watered down theory we used to teach our students.
I am trying to keep it simple [as it should be] for Mr. Gegory, who asked a simple question. I believe in keeping things simple stupid. Far too many people become intimidated by complex explanations of sailing theory, and become “Motorheadsâ€
Frank, with the greatest of respect, I kindly mention that I have seen some REALLY dumb things stated over the years re: boating and sailing.
The issue of rudder control by pulling water over the rudder is one of them.
The issue of breaking waves vs cresting waves is another (and a SERIOUS issue to boot), for breaking waves are HIGHER than surrounding waves AND are rotating all the way to the ocean bottom, while cresting waves are shorter than surrounding waves because the winds have blown the tops off the waves. Breaking waves are rare, rare, rare in deep water, no matter the stories one might read. Breaking waves can turn a large sailboat over sideways, cresting waves not even close.
(If you doubt that, consider that the wave height at sea of a tsunami wave is well less than a quarter inch. It is only when bottom depth gets to be less than about 1/2 wave length do the troubles of a tsunami waves become an issue.) (BTW, there is a reason offshore charts are marked showing the "Hundred Fathom Line" (now 200 meter line), for generally breaking waves are never seen at that water depth. Generally.)
The issue of DED (as in Deduced, NOT DEAD as in dead bang on center) Reckoning as anything but a very bad guess is another (another law of physics). (Pre-Loran/GPS, only 40 years ago, DED Reckoning sunk a LOT of recreational craft in reduced visibility conditions.)
And other issues. And other issues. And still other issues.
I'll say it one more time. A boat -- WITHOUT speed -- can NOT be steered by pulling water over the rudder. Can NOT.
Please, please, please, 40 years of experience (mine goes back to the late 1950's) or 40 minutes of experience, it makes no difference. SAFETY IS NO ACCIDENT.
Sailors tend to be the most superstitious lot I have ever seen.
Jim Gregory wrote:I just bought a CD 28 w/o a motor and wanted to know if anyone has experience with an OB on a 28. I think a 25" shaft will reach as low as the inboard prop.
Thx-JIm
No experience with a CD-28 but the Typhoon does very well with a small outboard. As long as you didn't go crazy with horse power and the associated weight you should be just fine.
My CD-30 only has about 16HP and it is more than enough. The inboard inboard might be slightly more efficient but that gives you a ball park of power requirements.
I see no reason why a long shaft motor in the mid teens for horse power would not serve you very well. It might depend somewhat on how you intend to use the boat. If you are going to be mostly day sailing with a short distance to where you could raise sails almost any engine would work.
If you kept it small enough and wanted to go to the trouble, you could take it off and store it down below.
For a long distance cruiser you might be happier with an inboard. For a boat that is mostly days sailed I believe the outboard would be fine.
Unless you can steer the outboard, don't count on any propulsion giving you great steering in reverse, Steve.
WaywardWind wrote:Frank, with the greatest of respect, I kindly mention that I have seen some REALLY dumb things stated over the years re: boating and sailing.
The issue of rudder control by pulling water over the rudder is one of them.
The issue of breaking waves vs cresting waves is another (and a SERIOUS issue to boot), for breaking waves are HIGHER than surrounding waves AND are rotating all the way to the ocean bottom, while cresting waves are shorter than surrounding waves because the winds have blown the tops off the waves. Breaking waves are rare, rare, rare in deep water, no matter the stories one might read. Breaking waves can turn a large sailboat over sideways, cresting waves not even close.
(If you doubt that, consider that the wave height at sea of a tsunami wave is well less than a quarter inch. It is only when bottom depth gets to be less than about 1/2 wave length do the troubles of a tsunami waves become an issue.) (BTW, there is a reason offshore charts are marked showing the "Hundred Fathom Line" (now 200 meter line), for generally breaking waves are never seen at that water depth. Generally.)
The issue of DED (as in Deduced, NOT DEAD as in dead bang on center) Reckoning as anything but a very bad guess is another (another law of physics). (Pre-Loran/GPS, only 40 years ago, DED Reckoning sunk a LOT of recreational craft in reduced visibility conditions.)
And other issues. And other issues. And still other issues.
I'll say it one more time. A boat -- WITHOUT speed -- can NOT be steered by pulling water over the rudder. Can NOT.
Please, please, please, 40 years of experience (mine goes back to the late 1950's) or 40 minutes of experience, it makes no difference. SAFETY IS NO ACCIDENT.
Sailors tend to be the most superstitious lot I have ever seen.
That is great. I still don't know what it has to do with the original question asked in this thread.
If you have any experience with a stern mounted outboard on a sailboat like a Cape Dory 28, than please help Mr. Gregory with his inquiry. If you want to prove you are really good at physics… then I think you have attempted to prove that at least a dozen times already.
But I fear that your B.Sc. in physics and mathematics from the institute of technology of a large, well-known, land grant university is getting in the way of your ability to understand the original question.
I fear I am encouraging your behavior by engaging you in this thread. [go back and read your posts to this forum over the last two years] than you will understand what I am talking about.
My two favorite quotes by you are “WaywardWind Posted: Mon 8/10/09 8:56 am Post subject: It's time to do more sailing.
I signed on this site when I bought a Cape Dory, a boat I have lusted after for 20 years. I very much had hoped to learn something about Cape Dory's and sailing in general.
I have been deeply disappointed. I am going to do some more sailing. And, in January, I will be part of a 500+ mile upwind ocean passage. “
And my all time favorite isâ€
Jim,
I had a 9.9 hp outboard on my 1979 Cape Dory 28 when I purchased it in 2001 in St. Augustine, Fl. The previous owner had removed a tired Volvo and opted for the OB on a bracket mounted on the center of the stern. It was a long shaft but I forget the exact length.
I knew I would be installing a Yanmar when I got it home to west central Florida but I put the outboard thru some tests in deciding whether to sail or truck the boat home.
I beg to differ with anyone who recommends any outboard for that size boat. I never had any inclement weather but with the motor opened up it would barely push the boat against an incoming tide. With the tide and wind against me I could make little or no headway. With a 1-2' chop the prop would be out of the water.
Granted, the motor was older, a loud noisy two stroke and a new 4-stroke would serve you better. But it was also ugly hanging off the stern, difficult to start and stop even with a push button.
It made my decision to haul the boat and have it trucked an easy one. No way would I rely on an outboard to get me 700 miles around the Florida peninsula.
I only got $200 for it which did not go very far toward the $5600 for the new diesel but it was still a no-brainer. Best of luck.
Kevin Mulligan
Cape Dory 28 #226, "Skibbereen"
Crystal River, Fl.
First off, I don't think an outboard hung off the transom of a CD-28 LOOKS good. In fact, I think it LOOKS terrible!
That said, an outboard on a heavy displacement boat HAS THE SAME PROP SIZE ISSUES as an inboard on the SAME boat.
_Most_ 8 to 15 hp outboards are propped for a planing rowboat traveling 10 to 20 mph. A prop for that size boat won't begin to allow the motor to rev up enough to obtain good horsepower.
The slower boat requires what used to be called a "power prop" and is now called a "high thrust prop", basicly a prop with about half to 2/3rds the pitch (and usually 4 blades)
Horsepower IS horsepower. That means with the right size prop for the application, the boat gets the very same horsepower, the very same performance. Outboard or inboard, no difference.
My CD-27 has a tired 7 hp (continuous rating) inboard engine. A tired 7 hp outboard (2-stroke or 4-cycle, no difference) with the proper prop would give the same performance.
HOWEVER, the blue sport coats at the Yotte Club would sniff at any outboard I might put on my boat. It would also ruin any resale value.
BUT it would perform the same. With the right prop.
btw, I've been using outboard boats since 1958.
btw, I've owned (and was pleased with) an outboard powered sailboat.
btw, I've sailed a CD-26 outboard and it sailed nearly as well as my heavier, longer waterline, deeper keel, more sail area CD-27 inboard.
btw, I would again buy an outboard powered sailboat without any hesitation.
btw, I do not belong to a Yotte Club.
btw, before I bought my CD-27 (which I love) two other and very similar boats were on my "short list", a Bristol 24 and Bristol 27. EACH of those boats are far better boats in the outboard (in a well) version than the same boats with an inboard.
My "second list" included Westerly 22's and 23's (because of their seaworthiness for cheap and ability to anchor "way to the back in the shallow water) and W-22's and W-23's are all now outboards (some came with inboards, but all were removed).
btw, my little bro for years wrote technical articles for the Experiement Aircraft Association, mostly about the dynamics of engines and foil fluid flows.
If Mr. Gregory wants to hang an outboard off the back of his CD-28, let him. Indeed, even encourage him, for he'll get sailing sooner and for far less dollar outlay. That's good, for the sailing is the same.
If Mr. Gregory wants to sell his boat at some point in the future, the boat is certainly worth no less than it is today. And if he wishes to choke down six or eight or ten thou -- like tamping sawdust down the throat with a stick -- to install a working and workable diesel, let him do that as well, for it is his decision.
IF the idea is to sail sooner for less money, an outboard on his boat is a viable solution. On the other hand, IF the idea is to restore a tired CD-28 to its former glory, that is a decision with all kinds of economic and emotional "I-gottcha's"
Generall, and certainly in today's market" it is far cheaper -- and certainly quicker -- to buy an already restored boat than it is to DIY.
btw, even with a peppy brand-new engine, my CD-27 STILL was trying to push well more than a thousand pounds of displacement for EACH horsepower. Today's boats generally have 4 TIMES that amount of horsepower for a given displacement.
btw, when Eric Hiscock first put a (cantanerous) THREE (3!!) horsepower motor in his 38 foot sailboat, he thought he died and went to heaven.
Let Mr Gregory do whateven he feels comfortable on his boat, and let the Yotte Clubee's worry about the creases in their white linen trousers.
WaywardWind wrote: ... I've been using outboard boats since 1958 ...
It's always pleasant to think back on the Eisenhower years: Elvis, Sputnik, Payola, Buddy Holly, the Checkers speech, Dienbienphu, my '56 Chevy, and of course, the inimitable Gogi Grant ( http://www.youtube.com/watch?v=uSPLSo3U46Q ).
WaywardWind wrote: ... when Eric Hiscock ... died and went to heaven ...
We certainly agree that Eric Hiscock has died and probably gone to heaven (lower case "h"). However, having read most if not all of his books (albeit quite a while ago), I remain to this day uninformed about his religious convictions and preferences. Indeed, there is even a finite possibility that he turned left at the heaven sign and has been reincarnated as an anchor or something.
WaywardWind wrote:
btw, when Eric Hiscock first put a (cantanerous) THREE (3!!) horsepower motor in his 38 foot sailboat, he thought he died and went to heaven.
--Eric Hiscock's boat wasn't 38 feet long. Wanderer III was 30 feet long.
-- The engine wasn't 3 hp. It was 4 hp.
-- He didn't think he'd died and gone to heaven. Quite the opposite. He was very disappointed: "That was a mistake," he writes in Voyaging under Sail, "for that engine gave her a speed of only 3 knots in smooth water and a calm . . ."
And on the question of maneuverability when a boat is not making way, Hiscock said:
"The screw-race sent aft by the propeller when it is turning to drive the yacht ahead will impinge on the rudder if the installation is central, making control easier and more certain even when the yacht has no way on her." (My emphasis.)
John Vigor wrote:"The screw-race sent aft by the propeller when it is turning to drive the yacht ahead will impinge on the rudder if the installation is central, making control easier and more certain even when the yacht has no way on her." (My emphasis.)
John V.
That is true, for under that condition, the prop PUSHES water over the rudder.
Trying to back up with the same prop config (forward of the rudder), the rudder is useless until the boat is actually moving.
I recently mounted an outboard on my CD 28 as a spare engine.
We've used our recently acquired CD28 more as a powered cruiser than a sailer, going down the ICW, with future plans for cruising the St Johns River, then down the ICW and across Florida via the canal, etc. Even our nearly new Yanmar 3YM30 can have problems: just before a leg of the ICW in NC we lost a raw water impellor blade into the heat exchanger. I elected to motor on, but my wife was not comfortable, dreading engine overheat in a bad spot.
Since that trip I found a Nissan 9.8 2-stroke short shaft with a Zodiac inflatable. The engine weighs only 56lbs. (short version:the Nissan/Tohatsu 9.8 2-stroke is a gem, now no longer made). I can carry the engine on the dinghy or mount it on a Garlick bracket I mounted on the center transom. I used plastic board outside and inside with big washers to spread the stress. The bracket has enough travel to keep the engine clear when raised, and can lower the engine enough to avoid cavitation (a couple inches below the cavitation plate). It looks fine to my eye and I can't notice any difference in handling, but my experience here is limited.
One possible mistake was buying the biggest bracket: the bracket spring is really hard to overcome to totally lower the engine. I had to stand on the handle to force it to the lowest setting. As I will hardly ever be raising and lowering the engine, and I now know how to muscle it down, this is acceptable. It's a very well made product.
I wish I could document more usage experience for the interested. I lowered the engine, pulled the starter rope and motored along at about 4-5 knots for a mile, steering with the tiller. Didn't go beyond 1/2 throttle. I was late for the marina hoist time and couldn't experiment more.
To give him credit, a salesman had urged me to try the engine with the prop "well lowered" before considering using a low pitch prop that would compromise its performance on the inflatable. He had gone down the ICW once on a heavier boat with a 6hp OB, no problem.
I carry the gas in the inflatable which I've been towing. Don't even notice it. For open water crossings I plan to carry the rolled up inflatable on deck and a very small gas tank lashed outboard.
If a person were really set on hanging an outboard on a mid-size Cape Dory, one at least to think about is a rebuilt six hp Seagull. (I don't think they made a larger one.) I had one for years that in an earlier life pushed a barge up and down the Oronoco River with it's big, slow prop. After that it pushed an old captain and his heavy wood smallish cutter around the Caribbean and the Chesapeake. Simple, strong, attracts knowing nods. Best for use into the wind because the Seagull has been called man's most efficient machine for turning fossil fuel into smoke. (10-1 gas-oil on older motors, 25-1 on newer ones). www.britishseagull.co.uk. Also, Rob Allan > Rob A <b_seagull@hotmail.com> has motors and parts in California.
