prop sizing 21EC

[jzois]

Team - Im getting ready to purchase a boat in spring 13. 21ec is close, but ive always had an issue w/ WOT speed (9-10 mph). Couple quick questions will put it all to rest....What is the duty cycle of running WOT (in case of foul weather emergency)? And would reworking the prop, or even changing the prop (from a reputable aftermarket dealer) a possibility to pick up 1-2 more knots?

John

 

[walldog]

You will find that changing the prop will not give you any appreciable difference in top end speed. That said, I would not hesitate to run the Yanmar 30hp or the 18hp at WOT if necessary in an emergency. You will probably find though that cutting back to 80% will not drop your speed much at all. 9 knots is about all you can expect. A squall will probably catch you in any boat. Just batten down, hang on tight and keep chugging along. These little boats are tough. My dog Jake and I got caught in a Norther in our original Willie's Tug. We got bounced around a bit, Jake moved in to the berth (Nearer to me), but we never felt we were in any danger. Jake may tell you otherwise.

Good luck in your search and welcome to the group.

 

[tlkenyon]

I have an aftermarket water temp gauge and can keep a close eye on the engine temps. I can run WOT for about 10 min or so before the temps get (IMHO) pretty high and approach the 205 alarm temp. Backing down just a bit - to about 3500 or so - keeps the temp high, but no too high, and I only lose a little speed. Re-propping will probably not do much good, as the speed is largely a function of the hull shape, even though the EC- is a semi-displacement hull. More HP will likely make the hull unstable in the water and just make a bigger wake and the stern squats deeper and deeper.

 

[rt11002003]

If I recall correctly, the Yanmar manual says 5 minutes out of 60 at WOT. All prop work will do for you is get the engine at its most efficient operating range. 🙂

Ranger made at least one R21EC with a 40 hp engine. Didn't increase performance enough to matter. It takes significant HP to get displacement and semidisplacement hulls to go fast.

When the weather gets bad and water gets rough speed is not a saving factor. One should reduce speed in bad conditions. As to out running storms, the fast moving ones will likely catch you unless your vessel is a high performance one. The best bet is keep an eye on the weather and operate accordingly.

My Rosbourgh RF-246 has twin 115 hp engines that can push the boat more than 25 knots. It was designed for the waters off Nova Scotia. But, when the water gets rough slower speed is much better and safer than higher speeds.

My R21EC was great in heavy air and hugh waves. One of the best handling power boats I've ever operated. My wife is not a boater; our lake is noted for rapidly changing weather. We were caught out in a big squall. She was really scared until she realized how well the boat was handling conditions.

gene