Sudden performance issues on new boat

[Manaz]

Hi all,

My family bought a Southwind SR17 (1992 model) with a Yamaha 115hp 2-stroke (with variable oil injection, same vintage) in November. We've had it out 5-6 times since, generally with 4 adults and 4 kids onboard (limit is 6 adults), generally with kids in the cabin and adults in driver/passenger/rear seats). It has been good so far, though I am not sure it performs or gets up on a plane the way it should.

I fitted a new Fishfinder today (Simrad GO7 XSE with TotalScan) and took the boat out for a quick spin to test the install (it all seems OK). We were three up - my father-in-law and myself (both just over 100kgs) in the driver/passenger seat respectively and my 8yo son (30kgs dripping wet) in the cabin.

As we got up to cruising speed (3k rpm or so is where I generally cruise - 4.5k rpm is where it seems to max out at around 30 knots), it started to kick up a LOT of spray from around the outboard itself, and I was hearing a rumbling sound that came and went).

I slowed down and it went away. I trimmed down the motor a little (I don't run it trimmed all the way down, tested another run, it did it again - and I was feeling a definite "roll" of the whole boat to port at the same time.

I played with the trim and doing some speed runs, and found my earlier trim level was about right - 5 knots faster at full throttle than with the outboard trimmed all the way down.

I found we got a lot of aeration when turning (particularly when circling back through my own wake) and even started hearing the through-prop exhaust at one stage.

The boat does seem to sit low in the water at the stern - I confirmed I had the bung in (I've made that mistake once before, thankfully we detected it very early), the bilge pump didn't throw any water when I tested it, and we weren't running with a full tank as I normally do (the 90L tank sits right on the centre-line of the boat, just behind the driver and passenger seat, extending to the rear seats). If anything, the boat seemed to be sitting lower ar the stern today than normal, which surprised me.

The skeg on the outboard has minor damage (trailing corner has chipped off). The sacrificial anode is doing its job, but is still mostly there. From what I can tell, my outboard is installed at the right height on the transom (see photo). The prop has a small amount of damage on one of the leading edged, but it is just a tiny dent, I don't think it would have this impact (it has been like this since we got the boat). There does seem to be some corrosion on the faces of the prop blades, I believe this could indicate a cavitation issue?

I am arranging to have the outboard fully serviced, and am seriously considering a new 4-blade stainless-steel prop.

Is there anything else I could/should check? Does anyone have any ideas why the sudden change of behaviour (the TotalScan transducer is big, but not that big...)?

[Manaz]

I can't seem to attach a file with Tapatalk...

http://imgur.com/9KHoqJ7

[mob0103]

Hi Mate, my total scan threw up a big rooster tail when I first installed it. That will be the spray you are noticing. Have a fiddle with the height of the transducer. Too low and it will plow through the water. I adjusted mine up and it is better. I don't think it would effect the performance of the boat very much though. Hope that helps.

With regards to your prop. I'm no expert, you can buy a new aluminium prop for around $150 to try and probably borrow a SS one on the premise of trying it to solve your problem

 

[Manaz]

The spray is coming up on both sides of the outboard, but I did give myself the ability to raise the TotalScan, so I will try that, cheers.

Might give Solas a call on the prop...

[Manaz]

The spray is coming up on both sides of the outboard, but I did give myself the ability to raise the TotalScan, so I will try that, cheers.

This is what the spray looks like (from a different boat):

Might give Solas a call on the prop...

[PaddyT]

Few things-I would of thought that motor should spin out to about 5000rpm if correctly propped and at correct height. Also dont discount the damaged prop- ok its got a couple of chips but is it bent out of shape a bit? that can cause a bit of a list so have a good look again at the prop. Really bad situation might be that you have water forward in the hull that doesnt drain out the through the bilge-worth a precautionary look - some FG boats can trap water leaking in from rain up in the forward sections , because they have underfloor bulkheads.

[Manaz]

The issue occurs with the transducer in the vertical position and it is clear of water flow there, so I am sure it is not the issue at this stage. It could also not cause the spray on the port side (the spray comes up both sides of the outboard, the transducer is mounted on the starboard side).

The loading of the boat changed too.

[Manaz]

Solas got back to me - apparently my outboard should do more like 5,800rpm at WOT, and they think the outboard is mounted 2 holes too low on the transom.

They're suggesting a S/S 4-blade 15P for $660 delivered, which seems reasonable...

[PaddyT]

Move the motor before you re-prop- you might be pleasantly suprised without having to spend $660- SOLas do know their stuff though

[Manaz]

noelm: Yes, I realise that. I may be relatively new to boat ownership (though I have spent a lot of my life on/around boats), I am not an idiot, I realise that outboards don't just change their mounting holes randomly without my involvement.

It may be that when fully loaded, the issue wasn't as apparent, but with a lighter load (particularly losing ~100kgs from the nose with 3 kids not aboard), that the inappropriate positioning of the outboard on the transom may be more apparent.

PaddyT: I suspect that is the path I will take. Starting to look into whether I do that myself, or get it done as part of what I suspect is an overdue service on the outboard.

[PaddyT]

All good mate- just change one thing at a time to work it out

[Manaz]

3 hours ago, noelm said:

Never tried to imply you are an idiot, just pointing out that "something" has changed, or, you have only just noticed the spray, remember, all we know is what you tell us, we can't see it, touch it, or test drive it, computers don't allow us to be there...yet!

Yeah, take note of the smiley.

The spray was definitely not there before - it was wetting down the transom quite a bit.

I think the biggest change has either been the number of people, or perhaps some prop damage (I took another look, it is showing more wear/dings than I thought, and I wonder if I didn't hit something floating in the water at the start of the last outing). I am going to remove the prop, give it a clean, clean up the shaft, re-grease and re-install - again, it's something that probably needs doing anyway.

Edited January 23, 2017 by Manaz

[Manaz]

Hi all,

So, upon close investigation, the prop's in worse condition than I thought.

The outer/trailing edges are actually pretty burred (this is new and must have happened on the last trip where I noticed the issue.  I must have struck something - which is odd, because the skeg isn't damaged any more than it already was).  The leading edges are, as I already noted, a little pocked.  What I've noticed upon closer inspection is that the cupped faces of the prop blades, there is a mix of what looks like surface rust and some "graining" of the metal surface - I suspect the latter is from cavitation).

The stock prop is a Yamaha 19-K.  Doing some research, quite a few people feel that the 19" pitch is "over-propped" for the boat/outboard combo.  Solas agree, and have sold me a 13.5x15 3-blade SS prop which arrives next week.  They also suggested raising the outboard - I can see it's been mounted higher before, which makes me wonder why it was lowered again, but I'll raise it again tonight and see how it goes tomorrow.  Then next week, I can put the new prop on and compare behaviour again.

I'll provide an update once changes are made...

[Raymondo]

Ah, the joys of boat ownership, at least your getting a fully immersive and expensive look into owning a boat early on. Lol. Just remember it's never to late to sell it.

[Swivelfish]

Good advice given here already i reckon, i had similar issues with my quintrex 5m cuddy when i first bought it. It sprayed from both sides of the motor..I loaded it to my specs with gear etc,  took her out and did some turns at speed..on a calm day..and got some cavitation. We lowered the donk, which sorted the cavitation, then becuase i was getting high rpm with less speed (like you!) i got solas to check the prop...the bush was shot and they re-cupped the blades. Shes sweet as now, i fitted a foil too. I still get spray when the donk is fully down, but this reduces when trimmed out, so i dont worry about it. Hope this helps bud.

[Manaz]

So, we took the boat out yesterday as a trial, to see how things would go.

For most of the day, it was mostly fine - still throwing up a bit more water than I'd like, but much better than the last outing. We ran from Kissing Point to Chinaman's Beach, and all seemed reasonably well - a bit of the diagonal spray, but I was able to trim most of that out. It was a bit choppy, so we didn't do any speed runs. We spent most of our time on or around 3k rpm.

On the way back, it was choppier (particularly passing the heads). I was adjusting the trim when we got the alarm tone from the outboard control box - oddly, only when I tried to adjust trim. Shut the engine off, checked both oil tanks, and they were both full. Tried adjusting trim, no power. Simrad GPS/Fishfinder shut itself down. Outboard wouldn't even turn over.

Odd.

Shut off the ignition competely. Shut off the electrical system with master switch, switched it all back on again - and everything fired back up - full trim control, outboard started first go.

About 20 minutes later, when crossing the wake of a Manly ferry (and hitting the swell with the bow quite hard a few times), we were back to hearing odd noises (including rumbling sounds and exhaust) as well as spraying water everywhere, and limiting travel to around 2500rpm. Didn't notice the "twisting" this time at least.

New prop from Solas arrives on Tuesday. My next door neighbour (who is an experienced ski/speed boat operator, having won a few comps over the years) thinks 15" pitch sounds very short (but acknowledges his use of a 28" pitch prop at times may impact his thoughts there - the shortest prop he runs is a 19" pitch), so we'll see how things go. I might get him onto the boat to see how it feels to him...

On the electrical side - when I installed the Simrad, I saw that there is a real mess of wiring under the dash, with lots of parallel circuits and poorly-thought out wiring. The instruments aren't working correctly either - I get RPM, but not trim level, fuel level or even running hours. I might have to spend some time (pretty urgently) getting things tidied up...

[Manaz]

On 27/01/2017 at 0:58 AM, Raymondo said:

Ah, the joys of boat ownership, at least your getting a fully immersive and expensive look into owning a boat early on. Lol. Just remember it's never to late to sell it.

Not selling.

Enjoying it too much (even with the problems and expense). The family are loving it too.

[Raymondo]

2 hours ago, Manaz said:

Not selling.

Enjoying it too much (even with the problems and expense). The family are loving it too.

Ha, your hooked. Some of my best and worst days in life have been on a boat.

[Manaz]

I put the battery onto the trickle charger - 5 minutes later, it was at full charge and trickling had started.  So the battery itself is fine.

The new prop arrived at work today.  I'm wondering now if the rubber bush inside the existing prop is potentially having issues - that may explain the change of behaviour after hitting a few big waves.

I'm also going to rewire everything I can in the boat (within reason).  The existing wiring is just too much of a mess.  I'll put a proper bus bar setup in (based on something like this: https://www.whitworths.com.au/main_itemdetail.asp?item=33492

[Raymondo]

Best thing about rewiring the boat yourself is if the proverbial hits the fan your familiar with the circuit and can hopefully fix/diagnose the problem. Bus bars make it easy to add or remove circuits later down the track., well worth the extra effort.

[Swivelfish]

Would be interested to know if u fixed this now? And what the issue was!

[Fishop]

I would also be interested to find out the end result here.  From my experience I get that sort of splash from trimming up to high.  So I would assume your engine is too high in the water with only 3 people on board.  However I don't seem to notice too much difference between having 2 people on board and a full boat with 6 people and a whole heap of fishing / camping gear.