Effect of blowing prop out of water

[paullee]

Hi been thinking about this for a while so thought I would ask the question. A few years ago I misjudged the tweed bar and got airborne in the process. All good went and caught a few fish but I’m pretty sure it was the week after this my etec limped home with what ended up being a gearbox missing a few teeth. Gearbox got replaced under warranty. So can anyone shed any light on what is the effect (if any?) of blowing the prop out of the water at speed? Anyone else with modern engines had any shutdown or limp mode problems while crossing bars? Pretty sure flooding carbies used to be an issue but what about these days?

[catshark]

any coota craft owners got a answer? there are videos of cootacraft and formula 233 launching off waves like missles, sure does look good but landing back in water surely is less forgiving than hitting hard surface areas like sandbanks,rocks and whales. perhaps your prop on re-entry managed to stress some cogs and the rest of the trip finished them off but really its a unknown.really the prop should off give up or bent or bush striped first off id be thinking.

[scottar]

If you didn't back the revs off on re-entry it was probably the cause. Take a look at just how busy the throttle man is on an offshore power boat

https://www.youtube.com/watch?v=6duN0vGIBkQ

[paullee]

Yeah ok real hard to say re backing off the revs but I imagine I would have. It’s along the same lines but I also thought having the prop/ engine go from full load to no load upon leaving the water would stress stuff Ike flywheel bolts etc etc...

[stevej]

seen two etecs many years ago with complete gear case ruptures ,the whole side of the gear case was gone
these were on yank bass boats and were being driven hard at speed and jumping wakes

would happen to any brand id assume high revs no load while airborne and then catastrophe on landing

big freighters have been known to split flywheels and props in big seas and running light

[Fed]

I thought they had rev limiters on them.

[stevej]

I thought they had rev limiters on them.

rev limiter wouldn't cut revs if boat was airborne
its more the shock of free spinning landing and the shock through the gear case when the prop bites again

[TheRealAndy]

I used to get air in my old polycraft all the time. It had a yam 50 4 stroke and I never had issues. I think my back would punch me in the back of the head if I tried that shit on these days though.

Current boat has yam 60's, they have been in the air a few times without issues, but its a pretty rare event. At least this one lands relatively soft when you jump off a big one. Props out of the water now are my signal to back off and/or manage the throttles a bit better.

[Fed]

rev limiter wouldn't cut revs if boat was airborne

Why wouldn't a rev limiter limit the revs when the boat was airborne Steve?

Rev limiter or not what I found was if I re-entered the water at WOT the props (cat) would pull air down with them and the boat would come to a stop with both motors revving their tits off & total ventilation like a couple of mixmasters.
I remember one particular day standing at the back of the boat checking out 2 motors at WOT & pegged on the tachos until it dawned on me that the props might grab some water by themselves and leave me swimming, I only did that once.
The only way to get going again was to back off & grab a fresh bite of water & hit the throttles.

On the other end of the scale I found if I backed off completely mid flight when the boat re-entered more often than not it would kick the motors up as if you'd hit something.

With some practice I found the happy medium of backing off & hitting the throttles just at the right time.

I'd suggest that's exactly what the guys were doing in scottar's video.

I seriously doubt being airborne would break a gearbox.

[GBC]

We used to be able to jump a mate's Vermont between swell tops inside the bar at Southport. The sweet spot was about 45mph. I can confirm a HPDI Yamaha does have a rev limiter and does not break gear boxes by becoming airborne.