Morning everyone,
Merlin is fitted with a Yanmar 3gm30F, KM3V v drive gearbox and kiwi folding prop which has been running fine all season. The PSS was replaced 2 years ago and has 23 hours on it and is not leaking. The engine and shaft alignment was set in May before we launched for the season. Engine revs are set at about 850rpm. In the last 3-4 weeks a problem has developed when I engage astern in that the engine either stalls or engages/runs at about 650 revs, struggling to pick up. If one attempts to increase the revs with the throttle it overpowers and loads of black smoke is emitted as it struggles to pick up. This means I can only move extremely slowly astern. Engaging and going forward is not an issue. The engine accelerates and decelerates normally when not in gear with no smoke.
I have dived the boat and the prop and shaft is clean, not fouled and the prop operates freely. The diesel filters are 18 months old with 23 hours use, the fuel was double polished at the start of the season. The bowl on the racor 10 micron filter is clean with no water or gunge. The tanks was cleaned out at the start of the season. The air filter has 23 hours on it and is clean. The throttle and gear cable are working correctly and set correctly and as they were at the start of the season. My exhaust outlet and elbow have 23 hours on them and are not leaking. The tank has a shot of Redex in it. The injectors were last serviced in 2010 with new nozzles. Merlin in currently on a pontoon and I was planning on a winters sailing!!
My thoughts are that this is not a fuel issue but either a gearbox or clutch problem. I would welcome some help on how I can identify the problem so I can fix it.
I had the identical issue (without the black smoke) with the Kiwiprop feathering prop beginning three seasons ago, and was able to finally resolve the issue last (2020) summer… I detailed the fix here: Transmission in Reverse - almost no revs (google.com) - or just search ‘Kiwiprop’ in the discussion group and you will see it with this title ‘Transmission in Reverse - almost no revs’ with a date of August 7, 2020.
What I found, while hauled out, would have been next to impossible to discover when diving on the prop, even if done with proper diving gear and not a snorkel (which I would guarantee would be impossible!). It was very subtle, and was still happening after the prop had been cleaned… the problem was where the notch at the hub side of the blade is supposed to pass over the triangular rollers… it is actually an easy fix when hauled-out.
I do have vid (somewhere) of the fix and would be happy to post a link if needed… let me know.
Peter Grabow
S/V CAKE WALK III
1987 30 Ultra 430
Jersey City, NJ
Thank you very much for this. I had the prop serviced and greased completely by KIWI in summer 2020 and it has only been in the water since May this year due to covid. I know the parts you describe well as I dismantled the prop once to lube it prior to its service.
The viz when I dived the boat with scuba was dire and I would not have seen this. I think I will dive it again to see if I can witness this process and if not get it hauled out.
On a side issue, I replaced the cutlass bearing in winter 2020. Someone had attached an ambassador AM10 rope cutter and drilled the securing screws into the cutlass bearing brass body which prevented it from being pulled out. The screws were nearly scoring the shaft! I ended up having to use a handsaw blade to cut through the body of the cutlass bearing (without scoring the P bracket) and then using a small screwdriver to lift the bearing out in pieces. Replacement was easy. I had a tool made up to remove it again if needed. I can send you photos when and if you need them.
Many thanks again,
Happy to try and shed some light… As Joe V mentioned, it must be either gearbox or prop due to the parameters.
As noted in my linked post, I had the transmission rebuilt (it was the original and was 33 years old at the time… with the transmission rebuilt, upon the trial run, had the same issue with stalling or low revs… so pulled the boat and did the prop cleaning. It wasn’t taking much to stop the blades from moving into reverse position… just a slight build up on the notches and the rollers, and this was after the bottom/prop/shaft were all power washed. It had to be hand scraped and then, as in noted in my original post, the notches were filed slightly to provide a bit more clearance.
With this said, I began to occasionally have the same issue again recently… I haven’t hauled the boat out since summer of 2020 when I corrected the issue. I must assume that there is a bit of growth in the wrong places causing the prop to bog down…
As I now know how to correct the problem, I am not very concerned, but will do a proper cleaning of the notches and rollers to make sure I do not damage the transmission or engine.
I have cleaned the prop while in the water using snorkel gear this summer, but this doesn’t allow for proper cleaning of the notch spaces and rollers. I also need to grease the entire unit again… this must be done every year.
This is a link to the dropbox folder containing the images and vids of the prop cleaning… the last two mp4 vids show in detail what the problem was and the after-fix…
Hi Peter,
Thank you for the update and the photos/video which are really useful in fully understanding the issues. I think my rollers are a different style to yours in that they are completely round but that aside I am going to get hauled out when I can get booked into an appropriate yard and see what is happening down there. I will post an update afterwards.
I dived Merlin again and did find an issue with the KIWI prop in that one roller was seized and there was not free rotation of the hub probably caused by silt/sand. Vectra Marine who sell and service KIWI props in the UK have been very helpful but it appears that this prop is not suitable for the waters I regularly sail or the drying pontoon berth I am currently in. The KIWI NZ site is quite clear about this. So I am going to reprop. I have sent the forms off with the key details and await quotes for a fixed blade bronze prop. One company have asked the question will a 17" prop have sufficient clearance? I cannot recall what the clearance is on my 16" prop is like under the hull. Can anyone with a 30U on the hard, tell me the distance between the centre of the cutlass bearing and the hull or more simply does a 17" prop fit a 30U with sufficient clearance. I cannot see my prop to answer this question!!
Thank you
Sean Curran
Merlin of Mersea #489 30U
BOSMBSC, Somerset, UK
Hopefully someone can answer you, Sean. However not only do you want clearance, but you want to avoid cavitation if the blades are to close to the hull. Most prop suppliers can help with that.
Joe Valinoti
S/V iL Gatto NS30U #221
Sea Harbour YC
Oriental, NC USA
Suggest you try Fex-o-Fold. They’ve done many on our boats. I replaced a messed up Autoprop with a 3 blade Flexofold and love it. With it I now have brakes which makes pulling into new docks a whole lot less dramatic.
Ed Strazzini
PELICAN N33#36
Deltaville, Va
Just for the record, there is 29cm between the centre of the prop shaft and the bottom of a nonsuch 30U. A 16" blade has a lot of clearance and a 17" blade will fit but the issue Joe raised on cavitation will need to be considered with the propeller manufacturer.