Propulsion Issues.-

[Sea Rider]

Scenario,

According to boater, boat was running at near wot, a fishing net was spotted up front, speed was reduced and gear was put to neutral. Spinning blades caught fishing net and became entangled on blades. Net was conveniently removed after some minutes work, now :

- Water pump is not working, no peeing whatsoever.
- Prop doesn't spin although gear mechanism can be shifted FNR while engine on.
- With prop removed, when shifted FR prop shaft stays dead, inoperative.
- Prop shaft seals are on.

Owner probably is not saying the thruth, he run acros the fishing net at 3/4 throttle and jammed the prop to a sudden stop due to fishing net entanglement. If so, could drive shaft splines, crankshaft internal splines be sheared or even breaking drive shaft somewhere due to such sudden extreme stop. ?

Happy Boating

 

[Silvertip]

Inspect the prop carefully for signs of a strike (any strike). Most fishing net frames are pretty light weight aluminum and I suspect the prop would slice through that easily at high speed althought he net material as stated, might get entangled. If the prop was aluminum, there would be signs of the strike. Here is why I suggest that. Some years ago I sold a 15 foot bow rider with a 70 HP Johnny to my neighbors boss. Several months later my neighbor asks if the transom was bad on the boat. Why I ask. Well the transom broke and his boss is expecting some compensation. He said his boss ran into a sand bar. Not my fault I replied. Well, my neighbor shows up one day to show me the now repaired boat and the engine was laying in the boat ready to be installed. After looking at the engine (specifically the prop) I asked who was driving the boat. Turns out it was his son but he stuck with the sand bar story. I said take a look at the prop! Does that look normal? Neighbor said whoops! The blades were folded to the point where they couldn't be used to mix a milk shake. End of story. The motor you reference likely hit something other than a fishing net. A fishing net would not likely strip the splines or break the drive shaft. I suppose something in the lower unit could have failed and caused secondary damage but again, I would suspect if that's the case, the part that failed may have been on the way out before the strike.

 

[robert graham]

remove and inspect prop and shaft....the prop may be "spun", or the rubber hub between the outer piece with the blades and the inner piece with the splines just sheared....depending on size/HP of motor, may just need a new prop....not sure about water pump issue but best to drop lower unit to inspect pump...

 

[Sea Rider]

Some clarification : It's a 70 HP 2 stroke Tohatsu engine with just 20 meterd worked hours. Was there when boater rocket from pier to open waters, after 5 minutes there was a radio call asking for towing services. When combo reached the boating club, personally inspected the prop, no visible signs of marks, whatsoever. No nada, prop seals are ok, removable hub is ok, nothing broken. The issue was a submerged fishing net, almost run into one last week...will run my boat over those careless fishermen if smething like that happens to me.

Thought for a moment he had a spun prop, as the prop shaft doesn't want to turn impossible to make a spun test. Prop interior splines are ok, no one is missing. Strange that water pump is not working while you can shift gears nicely with engine on, but prop shaft doesn't move a bit while giving juice. Engine revs good throught the whole throttle range. Can spin prop while at neutral

Was only asking if possible to rip off drive shaft upper splines or even break a drive shft at any given lenght. Will need to drop lower leg and check drive shaft, probably with issues.

Happy Boating

 

[robert graham]

I have broken a driveshaft once before on my 3HP Tanaka, but it was only about 3/8 inch in diameter....broke right at a machined step.....I expect the driveshaft on a 70HP motor is pretty stout, but who knows?....it's worth a check....

 

[Frank Acampora]

Since the water pump is not working and since it is directly connected to the drive shaft. There is a distinct possibility that the drive shaft has broken either at the splines where it enters the crankshaft or at a necked down portion if there is one. It is definitely time to remove the lower unit and have a look-see. There is also the possibility of internal damage to the lower unit. Sounds like an expensive 5 minute ride.

Judging from your description of the operator rocketing away, it is also a distinct possibility that he hit the net at full throttle too. You know: We all need to save face and will stretch the truth to do so.

 

[Sea Rider]

Frank,

Although drive shaft has a necked down shape at lower portion, if broken water pump will still be pumping which is not the case, so the issue aims at sheared drive shaft splines that achieves no water being pumped along no lower propulsion. Can you belive this new engine had fuel water issues that caused the internal bearings to rust and stick, all internal rotating parts were changed and now this net issue.

Boater was scolding with reason. 70 HP at 3/4 throttle on a RIB rated for a 50 HP is like going full throttle with a 50. Next week will pull lower leg, if it's a drive shaft issue it's near 500 bucks on that costly part alone.

Happy Boating