Bow thrusters, a bit like buses.....

[Javelin]

Not fitted one for ages and suddenly I have three to do.

The first is on a Southerly 39.
The owner ruled out a retractable one but wants to reduce as much turbulence as possible.
I recently saw a thruster that had no eyebrow forward but did have a large concave scallop aft.
It seemed to me that this would be far more hydrodynamic than the simple eyebrow albeit a lot more work.
Has anyone any thoughts on the pros and cons?

The 2nd one will be fitted to a Ovni 435.
Looking at a retractable swing door unit here but struggling to find the space in front of the diesel tank so might have to go for a vertical job and raise the bunk level a little.
Again any Ovni owners, past/present have any thoughts.

The 3rd is either renovation or replacement of a vertical retractable on a Hoek 51, originally controlled with a worm drive to raise and lower however it apparently used to stick so the worm drive was removed and so to retract is on a 5:1 rope purchase and gravity takes care of lowering it.
All a bit heath robinson so looking for a better solution.
Anyone had issues with a worm drive retractable system and did you fall over a solution?

 

[Javelin]

Decided to have a crack at the concave version I saw.
I've attached the photos of today's progress.
The first shot being of the one I saw down at Suffolk Yacht Harbour the other day.

 

[Jabs]

Its a beautiful job but seeing those big holes gives me the eeeeby jeeebies!

Neat and highly skilled solution!

Tony

 

[trapezeartist]

Sorry, but I don't like your chosen solution. The version that inspired you has very sharp edges on the concave area and I think they will generate vortices which will be very draggy. If it was all smoother with big radii, perhaps it would be as good an idea as the more conventional.

 

[Javelin]

I agree that the original has very hard edges.
For the record it was on a Southerly 100.

My version will be hopefully be quite a lot more hydrodynamic having a significantly longer scoop aft and will have softer edges.
The scoops were taken from the off cut of the new 8" thruster tube.
In hindsight they could really do with being cut from 10" tube or I could have just laid some up on a mould but that would have taken a day or so longer to do.
Currently my plan is that once I've built up the glass internally to around 20 to 25mm thick I'll be able to grind back and get a more sympathetic shape. (with any luck)