Twin KAD32 can't get over 12 kts

... in which case "fouling" (propellors / hull) might well be the culprit.

Trying to take a weed and barnacle farm with you never works well.
 
You make a good point, but the boat is copper-coated. So just has the slime on the hull, no weed or barnacles. Props are pretty clean too; certainly no worse than this time last year when all was well.
 
… but 3000rpm is 3000rpm. 12kts is not 24kts. The connection between the engine and the propellers sort of becomes fixed once the cone clutch engages.

It’s possible that the clutches are slipping, but that seems very unlikely - usually it’s a problem to engage gear.

It’s also possible that the propellor hubs are slipping. But again, a bit unlikely that both sides would have the same problem at the same time. Painting a line across the two hubs and the cone can help diagnose this. When I had slipping prop hubs, one engine went high revs, the other stuck at 2000rpm. So probably not that either.

I’d still check that you haven’t got a herd of giant squid clinging to your hull. Also that the drives are actually trimmed correctly, trim tabs working as expected. And check that your’re not carrying around a few extra tonnes of water that could have leaked into a hidden space. Open floor hatches etc to check down to the actual hull. Not the hull liner.
 
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Somerset Taz said:
So I will bleed them again next time I'm down to the boat to rule that possibility out - or fix the issue. Are there any top tips on bleeding KAD32 injector(s) please - I would like to be as sure as I can be that there's no air in the fuel system.
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If the engine starts and idles fine you do not need to bleed anything .
 
SC35 said:
… but 3000rpm is 3000rpm. 12kts is not 24kts. The connection between the engine and the propellers sort of becomes fixed once the cone clutch engages.

It’s possible that the clutches are slipping, but that seems very unlikely - usually it’s a problem to engage gear.

It’s also possible that the propellor hubs are slipping. But again, a bit unlikely that both sides would have the same problem at the same time. Painting a line across the two hubs and the cone can help diagnose this. When I had slipping prop hubs, one engine went high revs, the other stuck at 2000rpm. So probably not that either.

I’d still check that you haven’t got a herd of giant squid clinging to your hull. Also that the drives are actually trimmed correctly, trim tabs working as expected. And check that your’re not carrying around a few extra tonnes of water that could have leaked into a hidden space. Open floor hatches etc to check down to the actual hull. Not the hull liner.
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Yes. Its actually impossible to go 3000 rpm,s at 12 knots one day and 3000rpm,s at 24 knots another day regardless of the problem . The gearing is fixed .
 
Hiya Taz!

Do you put Diesel Bug treatment in?

Have you checked for bug?

Check your primary filters.

Just another thought, I went out last year to see how my Boat would perform if I lost an engine by leaving one on tickover and running on one!

I can’t remember precisely but I gave up trying to get more than 10knts

Knowing that both 32’s are running and revving up, have you checked they are both turning the props or you haven’t lost some blades etc?

A long shot but I would want to know to rule that out I guess.
 
aerobat said:
Yes. Its actually impossible to go 3000 rpm,s at 12 knots one day and 3000rpm,s at 24 knots another day regardless of the problem . The gearing is fixed .
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Again I'm grateful for the advice, although I'm a little confused with the comments about the revs vs speed. The problem I'm grappling with is that when the engines are at 3000 and at 12 kts it is still in displacement and I'm trying and failing to gain speed enough to get onto the plane. I'm saying when the boat was successfully up on the plane at 3000 revs, i.e. last year, it happily managed 24 kts.

I get the logic that this might point to extra weight or drag stopping the boat accelerating to a break out speed sufficient to get on the plane. Weight gain? The boat is not sitting in the water any lower than normal so I don't think it is a weight gain issue. Drag? A visual inspection, in the water, of the hull and props does not show any appreciable fouling either. It just feels to me that the boat is really down on power this year. It's been suggested I look at the turbo air intakes to see if the flapper/check valve inside the Y box is free to move.
 
Somerset Taz said:
The problem I'm grappling with is that when the engines are at 3000 and at 12 kts it is still in displacement and I'm trying and failing to gain speed enough to get onto the plane. I'm saying when the boat was successfully up on the plane at 3000 revs, i.e. last year, it happily managed 24 kts.
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This what we are grappling with as well.

The drive system between the engine and propellors is essentially fixed.

So if the engines are managing 3000rpm, it's not that the engines are down on power, it's the boat that is down on speed. Speed is good.
There must be some additional external factor outside of the engines to cause you to be stuck at 12kts where previously it was 24kts.

Whether that is something slipping, drive trim, missing propellor blades, fouling, herds of giant squid etc, who knows.
 
Can you try one thing when you are on the boat ?

When underway , leave on engine completely at idle at try full power with the other . Then repeat with the other engine and record rpm,s and speeds . There should be a difference between them both and we can learn which one is the weak one.

While hull fouling indeed affects performance its not so severe you would be stucked at 12 knots when normally the boats gets easily on plane .

One of your engines struggles after sc cutout . Take a close ear if/when the compressors actually cutout , a video would also be great .

I think we need to understand what actually is going on
 
You mentioned your boat hadn't moved for a few months since launch, at a time when marine growth can be at its worst, so I would definitely check the hull and drive gear. My other thought is something wrong with the turbos, you also mentioned the SC were serviced...maybe worth double checking and that nothing else has been affected around the engines. It seems odd that after liftout and service you now have an issue, but marine growth would be my first check.
 
Painting a line across the two hubs and the cone could eliminate "Slipping Prop Hubs" as a cause next time you are out on the water.
As above, a video of what's going on might help as well.
 
I've often been frustrated by forum posts that do not complete the story - leaving readers unsure what the solution was in the end. I can imagine sometimes this is because the fix was simple and/or due to an obvious own goal - as is the case in this instance!
Humble pie......
Last season, having slightly more slime on the hull when the boat came out, I was advised by Coppercoat that after a few years' use the coating sometimes needs light sanding to re-activate the copper in the coating. This I did and it was a horrible job. Very dusty and unpleasant when you are sitting under the hull doing it. It seems that whilst I did do a reasonable job on the hull waterline, as I got further under the hull and closer to the dust (!) the efficiency of my sanding and attention to the job must have tailed off significantly. So, whilst the sides, and perhaps the first 30 cm of underside, were not too fouled (as I reported in earlier posts) it was a totally different story for the rest of the underside. It was a veritable forest of weed and mussels - never seen as much growth!
So I thank, and indeed apologise, to all the forum members that helped me to check and rule out all possible engine issues.
In the end it was the fouling, equivalent to a (quote in SC35s' post) "herds of giant squid" was the culprit. Cheers.
 
I tried dry sanding conventional antifoul and gave up after about a minute. Wet sanding was more effective and although a little messy there is no dust to breath in. I used sanding mesh on a plate on a pole for most of the work. I would have thought wet sanding would be equally possible on copper coat.
 
Momac said:
I tried dry sanding conventional antifoul and gave up after about a minute. Wet sanding was more effective and although a little messy there is no dust to breath in. I used sanding mesh on a plate on a pole for most of the work. I would have thought wet sanding would be equally possible on copper coat.
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I used to do my own antifouling until some skinny kid from a professional company started doing a similar sized boat next to me at the same time - he was about 3x faster and got a better result.
I came home with antifouled ears, eyebrows, hair, and a Mrs SC35 that wouldn't go anywhere near me for several days.
 
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