What is the hull speed of a 26S withut the ballast and mass?

[Captain E]

I wonder if anyone has tried using the 26S without the Mass (removed from the boat). If so what is the hull speed? I would think the hull speed would change sincethe ballast is empty and the waterline and displacement would be different. The reason I ask is because in the potomac river where I sail, there are times no wind at all. (before I get yelled by someone about the need for ballast, I plan to do this with just me on board and mass removed,I don't plan to have 11 people on my boat.) be nice...

 

[Keith Nuttle]

hul speed

Since hull speed is a function of the square root of the waterline length and weight does not enter into the calculation, the hull speed would change only slightly. (square root of 26' (5.1) vs the square root of 26'6" (5.14) Note I dont know the actual measurements but doubt if you would gain much more than 6" of waterline length with the decrease in weight.)The difference would be the horsepower required to drive the boat to a plan.

 

[Dana H38]

Lighter is slower...

Unless you're severely underpowered, a lighter displacement will be slower, but only an insignificant amount. With ballast and mast your hull speed is approx 6.51 knots. Without ballast and mast I figure you'll be an inch shorter so your hull speed will drop to approx 6.5 knots.You'll likely burn slightly less fuel without ballast, but the boat will roll more and bounce over light chop. I found our M26D extremely tender without ballast water. The tanks are so easy to fill and drain that I recommend always filling them and enjoying the increased stability and smoother ride.

 

[Robspan]

More than hull speed

By hull speed, do you mean the theoretical limit, or the maximum speed the hull can attain if it planes?The theoretical hull speed, given about a 24 foot waterline length, is about 6.5 k. But these boats are light enough to plane and there have been a number of posts from people who have planed at much higher speeds than the theoretical limit. A couple of months ago, I crossed Galveston Bay at an average of 7.1 knots with a 30k wind aft. I also once, in calm air, revved up my 9.9 horse motor with the ballast tank half full and hit 8.1. I turned around and hit 7.5. The boat was trying to plane and pulling a big wake, like a motorboat before it gets up on the "step." With more horsepower, it probably would have planed. I suspect that the 26x was developed in part because MacGregor observed this characteristic.With enough horsepower, I suppose almost any boat will plane. But the expression "hull speed" means the max speed the hull will attain before it begins to plane.

 

[Captain E]

Mac 26 Classic as a Trawler?

Robspan, that is what I was thinking. I do remember a speculation thats how Roger Macgregor might have came up with the plan for the Mac 19 and Mac 26x. Ive hit 8.1 downwind, I don't remember if I was going down with the current or not. In the summer here, there is little wind and turning the a Mac 26C into a gas saving mini (minus the mast) trawler. I might only gain a 1 or 2 knot speed difference, but my power consumption on my outboard would be less since It would be minus 1200lb of water ballast to push. Hopefully I could double the distance a single tank of gas can carry. A bilge pump in the ballast tank would be a good idea. If somehow I get cought with the winds picking up I could fill up the tank and when it dies down, I could empty the tank. For now Ill keep my (mast up) since there is nice sailing to do. Don't get me wrong I love sailing, but when there is no wind expected in a 7 day forcast, I would like to motor, but with gas prices expecting to get higher, I have no plans or no budget for a powerboat.Makes me wonder if a 50hp with 200lb of permanent ballast in the cabin floor would make the Mac Classic plane? A new short rudder would be needed as the sailboat rudder might break and also adds drag at plane speeds.

 

[Capt. Kermie]

Hull Speed Misnomer

Those using the formula to calculate hull speed can also apply the formula to the 19, 26X & 26M and come up with similar results. Yet both the X & M & 19 will exceed the theoretical hull speed and will go faster at the same RPM without ballast, so weight is a contributing factor.The only way to know for sure is to borrow someones 15Hp or 25Hp outboard and see what speed you can do without ballast.There is the odd owner out there that has removed the mast and used the Mac 19, 26X & 26M as a powerboat. I know of one person for each model who has done it, I have with the M. Without any experience or knowledge of the 26S I would still speculate that Trawler speed (8-10 Knots) is doable with 15-25Hp and epmty ballast. It may be a bit corky in the chop but I doubt it would ever roll over.

 

[csobalvarro]

Differences in speed vs. weight

You're probably right about the speed being affected by the weight of ballast. But I don't think that's a function of the formula being wrong. Physics is pretty reliable Rather, the weight of the ballast actually changes the length at waterline of the hull, and that's the length that matters. I'm no whiz to be able to calculate the difference, but I know the nature of our displacement hulls is different filled vs. empty.