Hello. Does anyone know the max horsepower rating for a RK20 or a comparable 20 foot fiberglass sailboat? A really thorough and therefore hopefully reliable used outboard guy wants me to tell him the max horsepower rating of my boat before he sells me a motor, which seems like a good idea. I can''t find the coast gaurd rating plate on my boat and can't find any information on the web other than (LxWx.8)-15 = hp, which might not convince him. So I thought I would try the experts, you all boat owners. Thank you.
Max Horsepower Rating 20 ft sailboat
- Thread starter CAP"NADAM
- Start date
I had a Mac26S with a 5HP OB. 20 feet, you would be fine with something under 5hp. Maybe even electric or propane if you have restrictions in your area.
Sailboats don't have HP ratings like motor boats do.
A 20 ft sailboat will move quite nicely with a 4HP outboard. Sailboats are displacement hulls, adding more hp just means more weight, noise, and expense.
Shaft length is more important than HP.
A 20 ft sailboat will move quite nicely with a 4HP outboard. Sailboats are displacement hulls, adding more hp just means more weight, noise, and expense.
Shaft length is more important than HP.
Anything over about 5-6 HP would be a waste on that boat. ,My 25m footer runs hull speed at half throttle on the 8 hp, and my 21 footer uses 2.5 HP quite nicely
A good friend of mine runs a RK20 with an old British Seagull one cyl
A good friend of mine runs a RK20 with an old British Seagull one cyl
He's a brave man! Those things never start.
I still feel sad about the antique outboard museum on Saba Rock that was wiped away in the hurricanes. They were works of art.
+1 on that.
Back in rhe 70's I had a 7.5 HP aircooled 2 stroke from Sears on my Catalina 22. Not a very efficient engine but it was more than plenty. Who knows what weight and thrust the RK 20 transom will hold. If it was me and I was asked the maximum I would tell the guy 6 HP tops.
I think those were the most sworn at engines I've ever known.
i have a 3hp British seagull in pristine shape. 1965. i switched to a new/modern sparkplug, starts first pull every time. bought it with my 1948 Shell lake cedar strip 15' runabout with the kiekhaefer mercury rocket engine. the rocket is a tough on to get running, spews oil everywhere. any of you boys grow up with the rocket 7-1/2 hp racing engine?
sorry for the drift
Have you thought about a high thrust trolling motor? Or a smaller Torqeedo?
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If I were in the market for a new O.B., I'd consider an electric. On a small 20' boat, you could probably still get 100+ mile range on a charge. If you really wanted to go on longer cruises, you could add solar panels and stow a small Honda generator. But I really think you could plan a longer cruise with an electric O.B.
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If I were in the market for a new O.B., I'd consider an electric. On a small 20' boat, you could probably still get 100+ mile range on a charge. If you really wanted to go on longer cruises, you could add solar panels and stow a small Honda generator. But I really think you could plan a longer cruise with an electric O.B.
Thank you everyone for the information. This might be crazy but I'm thinking of having 2 outboards. Most of the time I wouldn't use both but having 2 makes me feel more secure. I want to go about 7 miles offshore to some islands eventually, so reliability and speed are important to me. My boat has a swing keel, so when lifted, and with mast and boom down, in an emergency, how much hp would be safe and how fast could I go? How much is hull speed affected by having the keel up?
Maybe even a better argument for electric and more battery reserve. I don't think the keel up will change your hull speed. It will reduce drag though
Hull speed or displacement speed is the speed at which the wavelength of a vessel's bow wave is equal to the waterline length of the vessel. As boat speed increases from rest, the wavelength of the bow wave increases, and usually its crest-to-trough dimension (height) increases as well
Hull speed or displacement speed is the speed at which the wavelength of a vessel's bow wave is equal to the waterline length of the vessel. As boat speed increases from rest, the wavelength of the bow wave increases, and usually its crest-to-trough dimension (height) increases as well
Thanks rgranger. I have thought about electric. Range was a concern to me but if I can go 100 miles on a charge then i'm much more interested. I would just need a what, 500 amp hour battery?Have you thought about a high thrust trolling motor? Or a smaller Torqeedo?
Torqeedo Motors | Inflatable Boat Specialists
We sell Torqeedo outboard motors and parts. Electric boating at its finest.
If I were in the market for a new O.B., I'd consider an electric. On a small 20' boat, you could probably still get 100+ mile range on a charge. If you really wanted to go on longer cruises, you could add solar panels and stow a small Honda generator. But I really think you could plan a longer cruise with an electric O.B.
Hull speed is a function of waterline length and hull shape. The centerboard will have a minimal effect on the top speed, but it will have a very positive effect on the boat's stability and help to stop any rolling or yawing.
Top speed without planning or surfing will be in the 5.5 knot range. A 15hp motor only push to about that speed, so will a 4 hp motor. The only time a little larger, say 5 or 6 hp motor will be better is trying to motor into a seaway. That little extra power help the boat recover faster from being stopped by a wave.
7 miles seems like a lot, however, it is only about a 2 hour sail. In good conditions that should be easy to do. Just watch the weather forecasts.
Top speed without planning or surfing will be in the 5.5 knot range. A 15hp motor only push to about that speed, so will a 4 hp motor. The only time a little larger, say 5 or 6 hp motor will be better is trying to motor into a seaway. That little extra power help the boat recover faster from being stopped by a wave.
7 miles seems like a lot, however, it is only about a 2 hour sail. In good conditions that should be easy to do. Just watch the weather forecasts.
Enough so that it is worth doing while racing downwind in centerboard boats. But pulling the board up won't turn a displacement hull into a planing hull.
I'm not sure why you would take the mast and boom down. Could you elaborate?
Maybe you should look for a MacGregor 26X (I think), which is a cross between a power boat and a sailboat. It will plane with the Rx'ed engine and it can sail.
Oh, i didn't realize the Torqueedo has its own battery. I research Torqeedo more. Thank youHave you thought about a high thrust trolling motor? Or a smaller Torqeedo?
Torqeedo Motors | Inflatable Boat Specialists
We sell Torqeedo outboard motors and parts. Electric boating at its finest.
If I were in the market for a new O.B., I'd consider an electric. On a small 20' boat, you could probably still get 100+ mile range on a charge. If you really wanted to go on longer cruises, you could add solar panels and stow a small Honda generator. But I really think you could plan a longer cruise with an electric O.B.
I figured that taking the mast and boom down, in the case that I had to motor to shore from the islands quickly, would help compensate stability wise for me raising the keel, thought it seems like my idea to raise the keel won't help me much. I guess I just like to think about options and ways to be safe because I am newer to the sailing side of boating.
At least you have sails to get you home. Imagine if you were in a stinkpot and it quit
If you need to get back in a hurry, don't waste time taking the mast and boom and securing them. Get in the boat and go.
Racers will raise the CB to go faster in a race, in a race hundredths of a knot in speed can make a difference between winning and losing. When cruising for 7 miles, it might make a difference of a few minutes. When motoring the difference between board up and board down has little effect on speed, just give the motor a little motor throttle to go faster. The board down increases drag which only means it takes a little more power to as fast with it down as opposed to up.