How do I _keep_ my first engine?

[dawktah]

I will be taking delivery of my first small RIB next week. I have rented a few in the past, but she is all mine! What I need to know is how do I keep the engine as long as possible and more importantly, out of the shop! Other than routine maintenance, I need to understand some of the basic do's and don'ts. It has been explained to me that getting the prop out of the water and the sudden loss of resistance of the water can damage the engine, and conversely, adding the resistance back after being out of the water can damage the prop/driveshaft. Assuming rpm stays constant. If this is correct, what rpm can it occur or does it even matter? Is it an engine size or type issue? Is this just something to be concerned about with the racing aspect of powerboats?

--Chris
Brig 450HL E-tec 60hp

[fast fred]

when you fly the hull off a wave, you need to let off the throtle, so the motor is decelerating, thats all. if you don't let off, when you get back in the water, about 9-10 gravites grab that prop, what usually happens is it rips the prop shaft out, it's funny. lissen for the exhaust, you'll hear it when she gets out , just back out of the juice till she gets back in, soon as she gets in you can light it back up. flyin wave is part of ribbin. new boat, nice.

[Andy_Rs600]

Originally Posted by fast fred

if you don't let off, when you get back in the water, about 9-10 gravites grab that prop, what usually happens is it rips the prop shaft out,

Not trying to sound bad, but have you ever witnessed this, or seen a boat/engine that this has happened to? I've never heard anyone say you need to easy off the power if the boat jumps, nor have i ever seen or heard of an engine damaged in this way. I drive 4.6m RIBs at work almost every day, as safety boats, and we have them flat out, jumping waves all the time with no ill effects. In the five years i've been driving there we have never replaced a prop shaft that i know of.

Further, there are some very good reasons NOT to ease off the throttle if the boat jumps.

[Nos4r2]

it's a bad idea to let your engine rev it's tits off out of water when you get airborne.It's not good for the impeller either. Not as bad now as before rev-limiters were common though.

[fast fred]

"it's funny" yes i've seen it, also frys the water pump, some Lu's can take it
better than others, but the Fact is if you keep stuffin your LU, don't matter if it's a number 6 merc drive, while the moda is accelerating it's guna brake some thing most likely the foot, basic boat mec stuff,

it is possable to light the rev limiter off when flyin which will save it for awhile.

buildin outboards all day, every day.

[Biggles]

I agree with Andy,

I get my RIB out the water all the time and don't ease off the throttle. It all happens so quick I can't understand how you would have time to ease off before landing.

The waves I go over are short sharp ones where you can just jump from one to another. I don't get chance to go on big rollers, maybe thats where you might ease off the throttle. Is that the case !

[Hugh Jardon]

i do try to back mine off if doing a jump but i find it is tricky getting the timing just right so as to back off just as you leave the water

so in the mean time i will just have to keep practicing like hell!

[Nos4r2]

Originally Posted by Biggles

I agree with Andy,

I get my RIB out the water all the time and don't ease off the throttle. It all happens so quick I can't understand how you would have time to ease off before landing.

The waves I go over are short sharp ones where you can just jump from one to another. I don't get chance to go on big rollers, maybe thats where you might ease off the throttle. Is that the case !

Yep- you're right there. There's not really time to back off over short stuff but if you can hear the revs rising dramatically there should be time to react and shut down the throttle. I do it quite a bit in mine-but the seas in Poole Bay tend to be more rollers and less like the solent chop.

[fast fred]

don't worry about the small stuff, "flyin it"


when you get some "hangtime"

[Andy_Rs600]

OK, to qualify my earlier post, and probably start more debate,

All the boats i drive have rev limiters, but i can understand the problem if you have an older engine without. Also, i agree it doesn't do your impellor any good to run with no water.

However, against this:

If the boat jumps, and you come off the throttle, the bow will land much more heavily than if you leave the power on. Thus it's a balance of risk to impellor vs risk to passengers.