Jet shaft through hull blowout

[tracerrx]

Very simply stated, a jet pump moving through water is a very complex system.

To simplify, refer to Rule 3 on your reference about pumps. The grates are specifically designed to a) avoid creating turbulence (or keep the flow laminar) and b) avoid restricting inbound flow (or create pockets with pressure that is too low). Both of these inputs are key to minimizing pump cavitation.

Now, if you intentionally did the opposite of my a) & b) above (as in: increase inbound turbulence and decrease inbound pressure), you will be increasing the chance of cavitation.

Unfortunately, the technical challenge of designing an inlet screen (a 2D design with many intersections and complex flow patterns) that minimizes inbound turbulence and maximizes inbound pressure is MUCH MORE DIFFICULT than designing a grate (a 1D design with no intersections and parallel flow patterns) to do the same.

Does that help?

heh heh.. Guess I should stick to healthcare! Guess if it was easy they would do this on PWC's.

 

[mark_m]

Had a close call this weekend. Asked the kids if they had the ropes secured..."yes"... Wife started the starboard engine to nudge us forward....
Engine quit almost immediately. I went to helm to investigate. It quit again immediately. Tried the port engine. Same thing.

Checked the ropes. Gave the kids my "this is not a cruise. you are the crew speech". Popped the plugs and found ropes around BOTH shafts.

Here is my question/comment. Why did the engines shut down on their own? Is there some sort of switch that does/could/should sense the extra resistance of something like a rope in there? Is that a feature or just a convenient disruption in the normal operation of the engine?

Anyway, I popped the plugs and pulled the ropes out with only a little effort and cussing and untangling. No need to get in the water, etc.

No other damage that I could see, hear or feel. We ran the boat all day after that with no trouble.


Good luck to the original poster on your repairs.

We're getting our sea legs.. Would like to get summary of the "you are the crew, this is not a cruise" talk, tailored for a 7 & 9 year olds... Strangely my younger daughter seemed more concerned about fenders and docklines than her older brother.

 

[Glassman]

Ok guys I think that the reason Yamaha puts hose there is for ease of manufacuring. If there is flex im my boat in that area it would severly damage all the bearings for the pump shaft. Another reason for the pvc is alighning the through hull fitting. When it pushed through it took all of the fiberglass it was scewed too. I would never get the hole drilled it the exact spot, there is some wiggle room in the fitting but not enough for me to be comfertable with. Im a master mechanic by trade but not a robot like they use to drill most of the holes in our boats. The pvc will be siliconed at both ends and fiberglassed at the hull end, that way if need be I can take it out if it does crack. I dont see that hapening in my lifetime. Pvc is broke down by UV light from the sun and that area hardly sees the light of day. Wish I was home working on it now, But Im in Littlerock AR for some Army schools wont be home till Friday.

I haven't followed your post in some time now.
After I read what you wrote above, I thought I'd toss out a recommendation if you haven't gone ahead and proceeded with your planned course of action.

Now, remember, this comes from an old guy who has spent a good deal of time around noxious chemicals known to shrink the brains of laboratory rats. (Good thing I ain't got no more laboratory)

If this unfortunate occurrence was inflicted upon me and my boat, I would disassemble the good side (there IS a good side, isn't there?) and I would take a mold of the cavity to replicate the exact shape of the hull in that location.

I would then, with that mold, build a part utilizing the same, or as close to I could determine to be the original build schedule.
Cut that part into the damaged portion of your hull and reinforce from behind as necessary, be as precise as possible with your measurements and that plug should be pretty darn close to original. Tight quarters to work in yes, but I've seen worse.

If that intrigues you and you want to repair the boat properly, I will be happy to expand on the above.

I do not recommend deviating from the Yamaha design and eliminating the flexible hose. Use a better hose perhaps, but I feel it should be a flexible part. You, might, since you are in there, reinforce the other side, but I'd chalk this up to a freak accident. I don't think you'll go through this again.

 

[TxChristopher]

Definitely a freak accident. I sucked up nearly 30 feet of a 4 person really thick Airhead bungee rope about a month ago and didn't have this happen. Killed the engines before they killed themselves though as soon as I heard that certain sound a rope makes when tightening on the shaft and it starts to drag on the engine. Not the first time either to eat a rope . . .. . . that rope of the OP's must have wrapped just the wrong way and the engine was not shut down quick enough for sure. Shit happens.

I wouldn't put pvc there either, pvc sucks in anything that vibrates or moves much at all.

 

[Cobra Jet Steering LLC]

Funny thing about ropes is they don't like props either, as for this situation in the future designate someone to watch the rope

 

[Ronnie]

I think adding a screen would cause cavitation because all of the metal crossing the front of the intake would disrupt the flow of water into the pump. It would also be hard to make the connection to the leading edge smooth. Perhaps Yamaha should take a look at what Mercury did on their M2 Sport Jets. I've had two Mercury engines mounted to Mercury M2 sport jets in different boats. They offered three different intake grates: (i) A "Surge Grate" which had 5 or 6 thin tines that folded inward a the leading edge (this was one of SeaDoo's answers to getting vegetation stuck on the grate or in the pump, that is, just let the impeller dice it up and spit it out, it didn't work well on rocks and the tines sometimes broke off), (ii) A standard 7 tine grate, the tines were thicker and fixed at both ends of the grate and the openings between them were thicker than the tines, (iii) A "Rock Grate" this had 11 tines that were thicker than the openings between them so the biggest thing that could get though was a tow rope but only if it was positioned perfectly.

I got my son to be more of crewman than a guest/tourist by getting him involved in selecting his own life vest and making a competition of stowing the lines. I also asked him to help me remember to do everything on my checklists, which made him memorize them (there are several, e.g. to launch, recover, dock, tube/wakeboard, etc.). Lastly, I gave him the job of first mate (even when Mom is aboard) when he is onboard and I make sure to let everyone know that he is a capable seaman so it won't hurt to do what he does or asks. At first I'd use letting him drive the boat in no wake zones as a reward for completing other tasks well (e.g. getting the dock lines out or putting them away with me asking or saying anything). Still even with all of this it took a few seasons for him to "get it'. By age 9 he could drive the WaveRunners and boat onto their trailers by himself. Now my only concern when we go out on the WaveRunners alone is being given a ticket because he is still underage for solo riding (he's actually a much better rider than most of my friends, more time on task I think).

 

[itsdgm]

I'd be afraid to put any screen in front of the grates. There's an incredible amount of pressure that is built up there. It won't be pretty if it comes loose because it only has one place to go and that's into the pump.

 

[Cobra Jet Steering LLC]

Year after year that same question pops up, There are many different types of intake grates Some are better than others however they all need to allow a lot of the water to get to the pump, every little restriction you add can collect weeds trash etc, the smaller the opening the smaller the trash that collects in it and the faster it gets blocked . I like top loader intake grates because they load the pump more evenly however they do not keep trash , ropes weeds out of the pump.
That's the operator's job, keep a watchful eye on the water and do your best to avoid running over things that can get sucked in the pump that will cause issues.

 

[Julian]

I am freakin' ANAL about watching for ropes, and so is my wife (thankfully). If you were paying attention on one of the "Squirt Gun" videos I took, you can hear her say something at the very end of the video like "Julian, we're heading over the anchor line" -which was true.....but so glad I had her awareness and understanding of the painful ramifications if you don't watch carefully!

 

[tdonoughue]

If this unfortunate occurrence was inflicted upon me and my boat, I would disassemble the good side (there IS a good side, isn't there?) and I would take a mold of the cavity to replicate the exact shape of the hull in that location.

Wouldn't you need the mirror image of the one on that side for the other side? I am thinking of the curve of the hull...

You, might, since you are in there, reinforce the other side, but I'd chalk this up to a freak accident. I don't think you'll go through this again.

I do think this is worthy of note. With how many times people have sucked things up on this board (the two most popular of which seem to be ski ropes and weeds), if this were a common thing that needed to fixed with reinforcement, I think many more of us would have had this happen. Another vote for freak accident.

Goodness, I don't even remember who the OP was, but however you fix it (even with the PVC), sure would like a report on what you did and the results of how it holds up.

 

[tdonoughue]

I'd be afraid to put any screen in front of the grates. There's an incredible amount of pressure that is built up there. It won't be pretty if it comes loose because it only has one place to go and that's into the pump.

Exactly.

And, if you do try to suck up something that is big enough, you will need to worry about it punching a hole in the chicken wire. Imagine your cavitation then. And if a chunk of it got ripped off...

I think I will stick with my grates and watch carefully. @Cobra Jet Steering LLC 's point in this regard is well-taken.

 

[cwoav8r]

@Glassman 's suggestion, and @itsdgm 's post makes me consider something else. I would be worried about any repair done there because of pressure as well. There is enough pressure in that area to blow out a clean-out plug, and there are some that have had the plugs come out with enough force to go through the swim platform deck... and this is INTAKE pressure... before the impeller. I never did quite get that... but...

 

[-klb-]

Stick you hand out the window at 40MPH and tell me there is no pressure. Remember, the boat isn't riding level, it is a few degrees bow up. That same pressure that is pushing the boat up on plane everywhere else is pushing water into the inlet, and it has a fair cross section exposed to forward momentum.

What the impeller does is draw from this pressurized inlet, and add even more pressure to force the water through the much smaller cross section nozzle, causing a huge increase in momentum.

 

[cwoav8r]

Hadn't thought of it like that... I was over thinking the suck part...

 

[rkluck]

Midlifecrisis, What did you end up doing and what were the results?

 

[MIDLIFECRISIS]

Have not worked on it in a while. Army stuff and blowing the turbo on my pickup last Wensday has put the boat on the side for a bit. Did put the new turbo and intercooler on my truck. Runs like a scared ape now. Pushed out about $3000.00 for the parts to fix truck. Glad I can do the work myself taking it to a shop would have broke the bank.

 

[rkluck]

I understand. I helped a friend a while back replace his turbo and it saved him a lot of money!

 

[justason]

..bump... still very curious on this subject

 

[MIDLIFECRISIS]

Been busy with other stuff and just started a new two car garage so we can expand our kitchen. When I get it back in my shop I will start uploading the post. Between the civilian job, the Army job and a 11 unit apartment complex I stay busy as hell.

 

[MIDLIFECRISIS]

OK finally got the boat back to the front of my shop. I'm still going with the pvc in place of the rubber hose. May even retrofit the other side. With the way everything is mounted from the engine to the jets there shouldn't be any movement, and if by chance I ever have another rope wind in backwards hopefully it will get tight enough to kill the engine. Here are some pictures. Ugly now but will get better.