Sumara’s Propeller

I’ve just finished painting my propeller. It does seem a shame to cover up all that lovely bronze, but I think it may be getting some really hard use this year. The wind in Scoresby Sund can often be very light. If there is a lot of drifting ice around then it can be very hard to steer a clear path whilst under sail, so motoring will often be the way forward. Johnston and Loftus Boatbuilders had the propeller specially cast in nickel aluminium bronze by Clements. This is a very resilient material both strength wise and for resistance to corrosion. The blade profile is quite chunky which I am hoping will be helpful if it hits chunks of hard ice.

Newly fitted in Ullapool
The propeller with the technical details

The last couple of years I have used anhydrous lanolin to guard against weed growth. It seems rather implausible, but it does actually work. In fact, this year I really struggled to get the lanolin off. I tried very hot water and washing up liquid with a scouring pad all to no avail. You could feel the slight stickiness after all my hard work, if anything I had just worked it in and improved its covering power. It eventually succumbed to acetone then aggressive sanding with 80 grit sandpaper.

At the end of the season, protected with anhydrous lanolin before the pressure wash

The lanolin had protected the prop against nearly all the weed growth but this year I want it to be spotless. I normally use a collar anode but the wrong one arrived and the replacement one was delivered a day after launching – typical! I could have dived to fit it, but I find collar anodes need a dab of Sikaflex over the bolts or the zinc erodes around the fixings and the whole shebang comes loose. I eventually decided to go without an anode for the 2021 season. It did result in a few minor surface spots of pink showing some dezincification, but all minor stuff.

After cleaning with acetone and sanding with 80 grit

This year the prop has had a coat of Seajet Propellor Primer and two coats of Emperor Antifouling. I will fit the anode before the launch. See the end of this post for some disappointing results!

Applying the Seajet two pack epoxy primer
Second coat of Seajet Emperor Antifouling

The great thing about long keeled yachts is that they very rarely get their props wrapped up with ropes. You could happily sail or motor over a line and it would just pop up behind you, there is nothing at all to snag it.

Being a small yacht is handy because I can actually change the prop under water. I had to do that in Guadeloupe in 1997 when the key in the keyway failed after reversing hard to get off a sandbank. Don’t ask why I was trying to get off a sandbank, but if they want to move the point when they change the direction of buoyage it would be handy to note it on the latest chart!

Talking about keyways, it is best to first fit your prop without the keyway. Ensure everything is spotlessly clean and whack the prop up the shaft and mark the furthermost point with some crisp masking tape. Avoid using a pencil as (apparently) the graphite can cause electrical corrosion. When you refit the propeller with the key in the slot, make sure the prop reaches the tape mark exactly otherwise it could be “keybound” and cause bad vibration.

The newly painted prop fitted with its anode nut

Technical Details

The preferred prop size according to Johnson and Loftus calculations was 14” x 7” but it wasn’t possible to get one made in Nickel Aluminium Bronze which was my preferred material, so we eventually went for 14” diameter with an 8” Pitch. It seems to work well – the little boat feels like a tug!

It was made by Clements Engineering

The shaft is 25 mm diameter from Sillette Engineering . The thread is M16.

The keyway size listed in the Sillette catalogue is 6 mm square x 55 mm long but the keyway on the prop is 1/4″ square. The old keyway measures 1/4″ so maybe it was a special shaft.

The engine is a Beta 16 hp

Update on Seajet Propeller Primer

October 2022

Well it didn’t work! After a few weeks in the water the paint just flaked off.

Seajet Propeller Antifouling system a few weeks after launching!

Maybe there is some reason why it flaked off but I followed all the instructions so it was a bit weird. This year I am going to try Hammerite Special Metals Primer. Normally I wouldn’t trust a paint below the waterline when you can wash your brushes in water, but I suppose science moves on and it can’t be worse than the Seajet primer. I will overcoat the primer with Trilux antifouling. More results next year!

The propeller cleaned and abraded ready for the new primer
The propeller cleaned and abraded ready for the new primer
The Hammerite Special Metals Primer applied to the prop

The Hammerite Special Metals Primer went on a treat. The picture shows it still wet, it dries with a satin sheen. Brushmarks just fall out. You can even wash your brushes with water. If this stuff actually works, it is quite a find. More news at the end of the next sailing season – October 2023.

Update 20th October 2023

The Hammerite Special Metals Primer was a total triumph!

For a waterbased primer this stuff is amazing! It looks like no part has failed, even the blade tips are still intact. The brown marks are just bits of weed that survived the pressure wash. All I need to do now is find an antifouling that will actually last a season. Any ideas?

One response to “Sumara’s Propeller”

  1. […] Sumara awaits on the pontoon before the lift out. We had to wait because I was minus one foot aground! Sumara after her pressure wash. All the slime soon fell off. The Hammerite Special Metals Primer was a total triumph! More about the prop can be found here […]

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