tomcat

Just finished reading the article on nitrous oxide for boats in Family Performance Boating. Several times the article mentions 25 HP/cylinder (200 HP) as a safe level. Tell me, what prop would you use if you added a 200 HP nitrous system???

[ 01-10-2002: Message edited by: tomcat ]

Holy Smokes

iTrader: (2)

I've read here before that nitrous is not good for boat engines. Don't recall the reason why??? Someone fill us in.

Vinny P

Nitrous oxide + boat motors = BOOM

In my opinion, Nitrous is not the way to get more power in any motor that you want to get some life out of. Nitrous works great for certain types of Drag Race cars like Pro Mods. They get a couple of runs out of a motor and it's tear down time. The main problem with nitrous is that you can only use it in short spurts. Not long enough to make a substantial difference in boats. I am sure that some guys will disagree with me, but the way I see it, if you are looking to go faster make horsepower the old fashion way. Cubic inches, induction system, cam, compression. And not neccessarily in that order.

tomcat

Here's the problem. If I added 200 HP to my engines, I would add 20 mph. If I didn't change the pitch of the prop, the engine would have to run 6250 RPM to reach the new top speed. Obviously this isn't a good thing, so I change the prop to keep engine RPM down at WOT. Now I would have a slug whenever not on the bottle. In fact the boat probably wouldn't get on plane, and would certainly be 10 mph slower as the engine struggled at lower than optimum WOT RPM.

This is the reality of nitrous oxide in single gear boats, and an article discussing the subject in a performance boat magazine should be pointing that out.

The best you can do is to limit the amount of nitrous oxide so you can live with a prop that is a little too big for normal operation and a little too small for nitrous operation. This is actually a good thing since it limits the amount of extra power period, and protects your expensive toy. It also makes the bottle last a little longer.

For my boat I figure that a 100 HP shot would add 10 mph and add 600 RPM. I have run the boat with Bravo 1 28" props for 82 mph @ 4800, and it's not a slug at all. Add 600 RPM and I would be at 92 mph @ 5400. I would not be afraid of short spurts at this RPM, and adding 100 HP to 500 HP engines is nothing to worry about.

For a similar range of WOT RPM a typical 24' Vee with a 454 Magnum would use a 75 HP shot and gain maybe 5-7 mph. So the rule of thumb might be to limit nitrous oxide to 20% of engine power and expect about 10% more speed.

Family & Performance Boating is a magazine that advertises a technically sophisticated format. The article in question missed a great opportunity to tell performance boaters something that they didn't realize about the possibility and reality of using nitrous oxide on their boat. I hope that they will follow up with an article that includes an actual test, and discusses these points.

In fact, if they want to send me two kits, I'll be happy to test them and write the article!

[ 01-10-2002: Message edited by: tomcat ]

Bruce

Tomcat, if you want to do nitrous on a boat, I'd suggest a three stage system with time delays or the prop will blow out! Shoot-out's are probably the best application, because the engine's are very thirsty for the juice. The engine's better be built to spin up, they love the juice!!

tomcat

Prop blowout. That's another good reason to limit the overall amount of nitrous. Three stages for shootouts makes sense. A small shot to help you get on plane with the big pitch, another shot to take you to redline with that prop, and the third shot to exceed all reasonable expectations of maximum redline. Sounds like a lot of fun, as Grandma used to say, right up to the time you put somebody's eye out with shrapnel.

Adivanman

Forget multiple stages, go with a progressive controller and bring a full 300Hp shot on over the coarse of ten or fifteen seconds. No prop blowout then.

Rambunctious

"....So the rule of thumb might be to limit nitrous oxide to 20% of engine power and expect about 10% more speed...."

For a power increase of 20% you won't see 10% gain in speed. The laws of physics won't allow. Power is a function of velocity to the third power (V cubed). so working the equation backward, and assuming your prop efficiency stays the same. for 20% more power you get 6.5% more speed (actually 6.265856 %) ( cube root of 1.2= 1.06265856) just physics........

Rambunctious
B.S. Physics
M.S. Mechanical Engineering

P.S. I did know an old guy who ran a 24 checkmate 10 years back with nitrous on a 454 mag around Holland and Grand Haven. He used to laugh so hard telling the stories about lining up to " these young punks with daddy's boat and their anorexic girlfriends try to race me, I'd play with them and when they thought they were edging me, I'd hit my nitrous and blow them away, tipping my hat and showing them my bald head and remaining grey hair......" August Vandam

tomcat

You are right, the speed increase would be less, I didn't think that out enough before writing. I have noticed that the cubed rule is complicated by the fact that boats operate at the interface of two fluids with very different properties. When cats in particular start to lift off the speed increase is significant as aerodynamic drag takes over from wetted surface drag. At 80 mph my cat is just starting to lift off as evidenced by porpoising. I hope that the extra power will drive through that point and hang the bow better. Is there anything more fun than applying physics and engineeering to high performance?

Rambunctious

You got that TomCat, just wish my job involved Product Development of Boat parts, not Car parts.......good luck with the juice.