How do I _keep_ my first engine?

dawktah · 13 July 2006, 22:28

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 · 13 July 2006, 22:41

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 · 14 July 2006, 00:02

Quote:

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 · 14 July 2006, 00:30

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 · 14 July 2006, 00:30

"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 · 14 July 2006, 06:30

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 · 14 July 2006, 07:12

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 · 14 July 2006, 09:04

Quote:

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 · 14 July 2006, 10:53

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

when you get some "hangtime"

Andy_Rs600 · 14 July 2006, 11:22

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.

fast fred · 14 July 2006, 12:01

as Captin , your first resposability is your crew, parts well thay are lower on the list, sounds like you are doin better than you think.

thare are some places whare you can buy an outboard of any year made
NEW, of any model from any maker, not only new, but better than new,
as in a SuperOutboard of any model ever made.

John Kennett · 14 July 2006, 12:02

Quote:

Originally Posted by Andy_Rs600

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.

If you're just bumping along that's fine, but it's not a good technique when things get a bit more serious -- you'll just end up landing the boat on its transom which isn't good for you, the boat or your passengers!

The knack is backing off the throttle to stop the boat launching itself off the top of the wave, then getting back on the throttle to keep the bow up for the next wave. It takes some practise, but feels great when you get it right.

John

The Garfish · 14 July 2006, 12:32

Quote:

Originally Posted by Andy_Rs600

it's a balance of risk to impellor vs risk to passengers.

wiv yew dryvin de bote bowf passinjers an impeller arr fukt. sownds lyke yew nead sum dryvin lessuns

Quote:

Originally Posted by Andy_Rs600

I drive 4.6m RIBs at work almost every day

i thort yew waz wan ov dem parrermedik nobburs.

spil de beens yew ratfink.

gaRf

wavelength · 14 July 2006, 13:41

so you take off the power as the boat flies off the wave-and it lands like a ton of bricks.
Leave the power on and you glance off the surface on landing and no-one gets hurt. Also keeps exhaust pressure in the leg and stops water swilling upto the powerhead on landing which is nice - particularly with a two stroke. Never had a problem with the lower unit or any other bit for that matter from landings-but I have acccompanied a crew member from a certain very official patrol rib to hospital after the helm throttled back in mid air , the boat landed dead and heavy and the crewman cracked a few vertebrae. New engine bits are far easier to find than new backbones. Of course the easy way is not to take off in the first place

or even dont go out in a boat

Hugh Jardon · 14 July 2006, 14:08

are we saying then never to throttle back at all when doing a reasonable jump

or

is it ok to back off the throttle slightly as you leave the water on a jump and have had all the thrust from the engine already, while in mid air throttle is eased back to stop the engine screaming too much but still backpressure in exhaust, then apply the throttle for when you land as the leg hits the water to keep forward momentum

what are we saying is best here?

i know what i do on a motorbike just interested to hear what folks think with a rib

Biggles · 14 July 2006, 14:25

My gut feeling is during normal conditions keep the power on. Having no power on when you land makes the boat stop dead. Its crew doesn't stop dead though, thats when it gets nasty.

Having said that if you can find a nice big roller where you can fly off better than Eddie the Eagle then I suppose it might be time let the power off slightly. I suggest these conditions are quite hard to find.

Andy_Rs600 · 14 July 2006, 14:27

Quote:

Originally Posted by The Garfish

i thort yew waz wan ov dem parrermedik nobburs.

spil de beens yew ratfink.

Yep, but i worked as chief instructor at a sailing club until very recently!

Quote:

Originally Posted by John K

The knack is backing off the throttle to stop the boat launching itself off the top of the wave, then getting back on the throttle to keep the bow up for the next wave

Agree competely, but the time to back off is BEFORE the boat leaves the water

like wavelength said. However, if you do jump the boat, through driving too fast, not reading the wave pattern correctly, or intentionally, if you come off the power you are in for a rough landing. Once the prop is out of the water, throttling back isn't going to affect the flight of the boat at all, only the landing.

When the prop re-enters the water, if it's at low RPM the leg will act as a brake. Because this prop centre of resistance/effort is below the centre of mass of the boat the bow will drop, and the boat lands flat, or even bow down, resulting in a hard landing or a full on stuff if you're going down-wave.

Conversley, power on in flight and when the prop re-enter it drives forward, and rotates the bow up, giving a nice soft landing.

Obvioulsy the best way is not to take off in the first place!!!

wavelength · 14 July 2006, 14:37

Quote:

Obvioulsy the best way is not to take off in the first place!!!

but it is fun isnt it-provided no-one gets hurt

. All crew instructed not to take the shock on the base of their spine but on bent legs lifting one's backside of the seat and to read the sea in front of them so it doesnt come as as surprise when they find the boat is airborne. Also to watch they dont headbutt the structures in front of them if the helm cocks it up and the boat stops dead. Running with the sea, trimmed up and some air under the boat-best feeling ever.

dawktah · 14 July 2006, 15:07

Great Info! I'll have more issues in November with waves than during the summer. I would assume the E-tec 60 hp has a rev limiter?

wavelength · 14 July 2006, 16:32

going back to the original question - flush it out after its been in salt water, and use the thing. Most engines on boats get sick cos they're not used enough. Best form of maintenance is running it-and its a lot more fun than having it sitting around anyway