Swan 43 prop
I have a 69 43 with a 3 blade 15" max prop. 5.5 knots at 2500 rpms is about the best i can expect….. as long as there isn't alot of wind or seas.
Ive had the yard adjust the prop settings a few times . not sure which is worse a prop that spins quickly with not as much pitch….. or a more agressive pitch that limits rpm and is rougher on the engine.
my only thought is to move the prop strut further back to allow for a 16- 18" prop.
my drivetrain is a perkins 4 108 with a velvet drive.
lars is there anything else I should consider. has any one had this issue with these boats.

Dear John
It is assumed the reduction ratio is the original 2.1:1.
Then 15" diameter is too small, and lack of blade area causes the problems.
17" diameter has been used on these yachts, and it is suggested that you check if this fits in, would bring 40% more thrust. 18" would be optimum diameter with the assumed configuration.
Kind regards
Lars

Thats the problem, 15 is too small. Unfortunately.the only way to get a larger prop in there is to move it farther back on the hull shape. Going to 17"-18'' prop would require the prop shaft strut being moved. The boat came with a folding 14" prop. I made the assumption the early 43's came with 14" props. Was I in error?
Is moving the strut a substantial project?
Thank you for all your help.
john

Dear John
Thank you for the information.
For some reason your yacht has a smaller prop diameter. The records suggest 17", and there are early 43's having this.
Moving the strut is a demanding task because correct alignment after the operation is a prerequisite, and I would suggest another approach - make room by carving away material from the skeg above the propeller. The skeg is solid, and the affected area is near its forward edge, check the thicknesses there. 3/4" thickness would be sufficient after the operation is finished, and laminate can be added on the inside as required.
Kind regards
Lars

Lars thanks again for the suggested solution. In your opinion would a feathering 15" - 4 bladed prop have the potential be a decent/ partial solution to my small prop size dilemma? Am thinking the additional blade area provided by the fourth blade could at least partially compensate for the diameter deficiency.

john

John
Yes, four blades would be a decent solution, gives about 30% increased thrust.
Suggest you set the pitch to 24 degrees, should allow the engine to reach a little over 3000 rpm max.
Would appreciate to hear about the result.
Kind regards
Lars

Thank you Lars. Will do .
john

PS
It is suggested you check if a slightly larger diameter would fit, this improves things. A diameter change affects pitch.
Lars

Thank you Lars. Will do . john

Hi John
Don Chisholm here. I own Zeevogel a 71 43 hull #49 out of Vancouver Canada and I upgraded this spring to a Max Prop Easy 18" set to an 11" pitch. I have a Perkins 4-108 with a Borg Warner. I'm very pleased with the set up - I'm getting approx 6.5 kts between 2200-2300 RPM and 7-7.5 kts at 2400 RPM with a ton of thrust.
Lars is correct with the need to have an 18" prop. I talked to Max Prop about the advantage in going with the 4 bladed Easy and they talked me out of it as the difference in performance is small - the advantage with the 4 blade is balance.
Moving your strut would be a massive project - strange why you don't have the room for an 18" prop - I had my strut rebed because of movement and it cost me $7K at a yard (not a cheap yard but still a big job) The 43 is a beauty BUT she has limited room to work in the stern costing more time / money to repair.

All the best, Cheers

Don
Thanks for your insights.
The boat came with a 14" prop. I felt I was pushing my luck ( according to clearance specs.) going to 15. Moving the strut or reshaping that portion of the undersides for clearance is a big project, My prop shaft is !" diameter, is that consistent with yours?
I will revisit this winter project when the boat is out of the water for a bottom job.
Thanks again
john

Don Thanks for your insights. The boat came with a 14" prop. I felt I was pushing my luck ( according to clearance specs.) going to 15. Moving the strut or reshaping that portion of the undersides for clearance is a big project, My prop shaft is !" diameter, is that consistent with yours? I will revisit this winter project when the boat is out of the water for a bottom job. Thanks again john

John
My shaft is 30mm. I've had my Swan for 20 years and the really of boating is taking each year...one after another with respects to money - if you bought the best gear for the Swan whenever she needed it - you would be broke. I have a yearly budget for maintenance and gear updates so I plan out what I want to do to the boat throughout the winter - it keeps me thinking about the boat when she's under winter cover.
Happy Sailing.

John & Don
Can confirm that the original Swan 43 shaft diameter is 30 mm.
With a 3-blade propeller having proper diameter there is no efficiency gain going to 4 blades.

Don, if you would like to have a Speed-Consumption-Range diagram made for your yacht you need to measure a number of rpm-speed combinations accurately in deep water. Say six readings distributed over the normal cruising range, one of them at full throttle.
Kind regards
Lars

John & Don Can confirm that the original Swan 43 shaft diameter is 30 mm. With a 3-blade propeller having proper diameter there is no efficiency gain going to 4 blades. Don, if you would like to have a Speed-Consumption-Range diagram made for your yacht you need to measure a number of rpm-speed combinations accurately in deep water. Say six readings distributed over the normal cruising range, one of them at full throttle. Kind regards Lars

Lars
Thanks for your input. I would be interested in creating the speed consumption range chart for Zeevogel. I've included a sample chart, is this what your what your suggesting.
If you could give me a bit more details on the how to measure?, that would be great - if I'm tracking with you...I would run the boat at different RPM ranges for a distance (what should that distance be?) and record the speed over that distance (would I then average that speed?) - should I do this on a completely slack tide?
How do you create the chart - is there a program to do that? Sorry for all of the questions. This should map out the RPM range to speed to fuel consumption - correct?
Thanks in advance. Don

Don
Yes, your diagram would be very similar to the one shown. The diagrams delivered with the newer yachts are based on accurate measurement of rpm, speed, and fuel consumption.
In your case a set of rpm/speed readings is needed, the consumption will be estimated, unless you have the possibility to measure this. The fuel tank capacity is also needed as input.
If you have a calibrated speedometer it is sufficient to run at each rpm for a minute or so, enabling the speed to stabilize. If you use GPS it is usually necessary to run in two directions and use the average.
When you run the full throttle lap it is recommended that you keep an eye on engine temperature.
The suggestion is to use a portable rpm counter with better accuracy than the engine panel counter.
The diagram is made with Excel, and can be customized for Zeevogel, including for example recommended minimum and maximum continuous rpm.
Kind regards
Lars

Don Yes, your diagram would be very similar to the one shown. The diagrams delivered with the newer yachts are based on accurate measurement of rpm, speed, and fuel consumption. In your case a set of rpm/speed readings is needed, the consumption will be estimated, unless you have the possibility to measure this. The fuel tank capacity is also needed as input. If you have a calibrated speedometer it is sufficient to run at each rpm for a minute or so, enabling the speed to stabilize. If you use GPS it is usually necessary to run in two directions and use the average. When you run the full throttle lap it is recommended that you keep an eye on engine temperature. The suggestion is to use a portable rpm counter with better accuracy than the engine panel counter. The diagram is made with Excel, and can be customized for Zeevogel, including for example recommended minimum and maximum continuous rpm. Kind regards Lars

Lars
Thanks for your comments. Got it!
Cheers