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S&S Swan General - Prop for Swan 40 Perkins 1.08
26 February 2018 - 10:34
#1
Join Date: 14 May 2017
Posts: 31

Prop for Swan 40 Perkins 1.08

Hi,

A bit of advice about a replacement of my old and original folding prop of my Swan 40 would be very welcome. The main reason is that the Perkins seems to be very low in its revs. Even when going upwind. Normally I never reach over 1500 revs. When giving more trottle the Perkins starts to smoke black. Seems that the boat is at hullspeed then. When increasing trottle the revs are going up a little but resistence is increasing more. The injectors are just being tested and are 100%. Another thing is that in reverse the engine needs much more revs to get some speed en steering control. That is because of the structure I read in another thread (Kiwi prop). Now I am looking for advice for a new replacement prop. 

Jolling Lodema, Swan 40 #22

26 February 2018 - 17:29
#2
Join Date: 02 January 2008
Posts: 1347

Dear Jolling

If your propeller limits the Perkins to 1500 rpm, you have about 20 hp max available.
This is not a big problem in smooth water, you loose only about ½ a knot of top speed, but in a strong headwind there may be insufficient power.
The recommendation is that this engine should reach 3000 rpm.
With a folding prop it is necessary to increase the rpm for achieving the same thrust in reverse.
You can find useful propeller information in the Forum Maintenance section under Comments on propellers
If you would like to have a recommendation for propeller dimensions the reduction gear ratio is required, as well as the maximum propeller diameter that fits.
Kind regards
Lars

27 February 2018 - 05:28
#3
Join Date: 03 March 2007
Posts: 190

Hi Jolling,

I have a 15 inch Kiwi prop on our 40 coupled to a circa 50  hp jhe  Yanmar.  I have been relatively happy with it although I think I am a little under proped.. The folks at Kiwi call it an unfortunate match due to the tranmission.. I purchaced the prop for another motor...Anyway,  I have adjusted it to achieve the max effect but am at the limit.  I believe they now have a 15 1/2 inch prop which might work better.  There is just enough space for it I believe but the clearance is tight..and turbulence is an issue.  

Best bet is to talk with the guys at Kiwi about this. They give excellent advice and will need info on the boat (the UK folks have ours on record) gear ratios etc and suggest prop size and adjustment of angle of the blades.  

 

By the way this prop is amazing in reverse!!

How is it going with the spray hood situation?? do you need more measurements??

 

Fair winds..

Mike from Stormsvale

Swan 40 hull #28 

 

 

 

 

 

27 February 2018 - 12:02
#4
Join Date: 14 May 2017
Posts: 31

Dear Lars and Mike,

Thanks for your advise so far. Maybe good to say the original Perkins 4.108 with its orginal Borg Warner transmission is in the 1971, S40. Yes, I saw the information in the forum about the propellors. But, I didn't see anyone with same engine/transmission combination. So, I was wondering what would be a good starting point for choosing a prop. I am considering a Kiwi or an Maxprop. In the forum I also found something about the reduction gear ratio. It might be 2.10:1 . But that is for a Swan 43 or 44 I believe. Maybe it is the samen foor the Swan 40?

About the sprayhood situation. Next friday the sailmaker comes to measure things. That will work out for sure. Making slow progress with the rest of the work. I will post updates in de the Swan 400S&S facebook group! It is too cold to work on the bout now!

Wille post a picture of my propeller soon!

Kind regards Jolling Lodema

28 February 2018 - 16:13
#5
Join Date: 02 January 2008
Posts: 1347

Dear Jolling

It is suggested you look for a manufacturer plate on the transmission stating the reduction ratio.
If not found it would be advisable to measure the engine and shaft rpm with a portable meter.
Kind regards
Lars

11 March 2018 - 07:19
#6
Join Date: 14 May 2017
Posts: 31

Dear Lars,

Yes, that is the best thing I can do. I looked for the plate but didn't see it. Probably it is not there anymore. I will try to find the gear ratio the other way around. But for this year I decided to leave the prop. There are so many things to do!

I made some pics of the propellor and measured the diameter. It seems to be 40 cm or 16 Inch. Considering to go to a Kiwi prop next year! Read good things about that one!

11 March 2018 - 08:12
#7
Join Date: 02 January 2008
Posts: 1347

Dear Jolling

Thank you for the photos.
Your propeller is a Varifold. Can you find the diameter and pitch marked on the hub or blades? With these numbers and your reported performance the reduction ratio can be estimated.
Kind regards
Lars

11 March 2018 - 21:39
#8
Join Date: 14 May 2017
Posts: 31

Dear Lars,

Thanks for your help. So good! I will take a look next weekend!

Kind regards, Jolling

16 March 2018 - 00:20
#9
Join Date: 31 July 2007
Posts: 71

Dear jolling

I want to buy your propeller  

P.J  

 

25 March 2018 - 20:00
#10
Join Date: 14 May 2017
Posts: 31

Dear jolling

I want to buy your propeller  

P.J  

 

Hi Peter,

Thnx for your offer. Probably I will not change the propeller this season. I need some more time to make the right decisions for a new one. 

Kind regards, 

 

25 March 2018 - 20:09
#11
Join Date: 14 May 2017
Posts: 31

Dear Jolling

Thank you for the photos.
Your propeller is a Varifold. Can you find the diameter and pitch marked on the hub or blades? With these numbers and your reported performance the reduction ratio can be estimated.
Kind regards
Lars

Dear Lars,

Last weekend I have been at my boat and I found out the specs of the propeller. Indeed it is a Varifold. It is written on it. And the size is 16/10/L. 

This season I will not change the propeller. I will clean and polish it, change the rubber bumpers and fit a new Zinc Anode. This summer I will do some measurements. I will make a curve for with RPM's at different boat speeds. Next year we can do some calculations for the right propeller.

Thnx so far every one.

I wish you all a good sailing/summer season!

Jolling, Swan 40 #22 Becca

18 April 2018 - 04:24
#12
Join Date: 31 July 2007
Posts: 71

Dear Jolling:

I have a boat like yours 040/012 with a Perkins 4-108 and the same gearbox. Here are my propeller data: All speeds are from GPS

Propeller 13 in dia, 10 in pitch, 3-bladed  Mfg. Michigan Wheel

1450 RPM    5.8 Knots

2000           7,2

2500           8          some smoke

2700           8          some smoke

3000           8          some smoke

3100 RPM    8.3 Knots much smoke, transom buried

This was with a clean hull, fresh from the yard bottom painted.

But I found that at about 4.5 knots under sail the prop starts to turn and this annoys me. So I installed a folding 2-bladed prop 15 dia x 11 pitch and run at 1450 RPM giving me about 5.3 kn with a clean hull.

 

19 April 2018 - 12:38
#13
Join Date: 02 January 2008
Posts: 1347

Dear Peter

Thank you for the information.
It can be concluded that your reduction ratio is about 1.5 to 1. 
Jolling's propeller has bigger diameter, and absorbs roughly twice the power compared to your 3-blade. 
He reported that maximum 1500 rpm can be achieved, this indicates that his reduction ratio is different, and about 1 to 1. 
Smoking at full throttle would be reduced if you adjust the engine high idling rpm to 3380, it was probably set to 4480 originally, i.e for hi-speed planing craft applications. There is a screw for this on the injection pump.
Kind regards
Lars

08 May 2018 - 18:24
#14
Join Date: 14 May 2017
Posts: 31

Dear Peter and Lars,

 

Thanks for the helpful information. Sorry I react so late. I didn't notice there were new messages in this thread. In the meantime I found out something about my engine. After adjustment of the valves it runs much smoother at idle and there is less smoke. Ia also found out that the RPM gauge is not correct. I used an Iphone acoustic app, that seems to give me the exact RPM. In earlier post I wrote about the 1500 RPM max. That is not correct. It is the max RPM with no smoke with the wrong gauge indication. I will do soon some new measurement at different speeds en RPM's. I come back to that. That will give probably better understanding of my gear reduction.

Abpout the screw. Yes I will adjust to the max idle you suggest Lars and see how it works out. 

The good thing is , the Swan is in the water and she is doing so well.

Thnx Lars and Peter!

Last weekend!

09 September 2019 - 18:21
#15
Join Date: 14 May 2017
Posts: 31

Dear Peter

Thank you for the information.
It can be concluded that your reduction ratio is about 1.5 to 1. 
Jolling's propeller has bigger diameter, and absorbs roughly twice the power compared to your 3-blade. 
He reported that maximum 1500 rpm can be achieved, this indicates that his reduction ratio is different, and about 1 to 1. 
Smoking at full throttle would be reduced if you adjust the engine high idling rpm to 3380, it was probably set to 4480 originally, i.e for hi-speed planing craft applications. There is a screw for this on the injection pump.
Kind regards
Lars

Hi everyone, hi Lars,

Yes it is some time ago since I posted in this thread. I am still planning to get a new prop for my Swan 40 during next winter. The Varifold 16/10/L there is on the bopatd now is not performing well.

A few weekends I did some measurements

Circumstances:
Light headwind (3 bft)
Small waves: (25 cm)

RPM        Speed (knts)
@1050    3.9
@1250    4.9
@1450    5.7
@1530    6.0
@1650    6.4  (light smoke)
@1725    6.7  (smoke)
@1800    6.8  (more smoke)

Max RPM: 2100

The prop seems too big for forward sailing forward. Backwards realy high revs are needed and there is a huge prop-walk. I am considering the following props:
- Maxprop (1 choice; better backwards, acceptable under sail)
- Kiwi prop (2 choice; good experieces at Swan 40)
- Flexofold (3 choice: god under sail and forward. Less good backwards)

Lars: Maybe you can help me little choosing the right prop and right size and pitch.

Of course advise is very welcome

Kind regards, Jolling (Swan 40 #22, Becca)

10 September 2019 - 12:53
#16
Join Date: 02 January 2008
Posts: 1347

Dear Jolling and Peter

Thank you for the measurement results, have plotted them (see attachment) for comparison, but there is too little difference. The Varifold should clearly produce more speed, and Michigan less. I would suggest both to measure again, with particular attention to:
- Deep calm water, over 10 m. If there is wind, the average of readings against and off the wind should be taken.
- Clean bottom and propeller
- Preferably log as well as GPS speed readings, rpm gauge calibrated.
 
Calculation shows that the 16x10 Varifold would require a reduction ratio if 1.82:1 in order to allow the engine to reach 3000 rpm. Alternatively - but not as efficient -  reduce its diameter by machining off the blade tips for getting the mentioned rpm, but for determining how much the present reduction ratio is required. If you decide to order a new propeller this ratio also needs to be specified.
It was mentioned before that the present reduction ratio is near 1, and unfortunately this is unsuitable for this application, and results in low propeller efficiency and additionally early cavitation for the propellers with flat blades.
The Varifold gives good performance, maybe a suitable second-hand reduction gear would cost about the same as a new propeller.
 
All Swan 40 owners are invited to report RPM/speed readings, I will then plot them and comment. This information is helpful for evaluating how the propeller is matched to the engine.
Kind regards
Lars

10 September 2019 - 16:42
#17
Join Date: 31 July 2007
Posts: 71

Thank you Lars and all others but I can't help to observe that our boats are sailing vessels and while a discussion about the very best propeller is interesting, the important thing is how well the noat sails. And it does that very well. If there is wind I sail. If there is absolutely no wind we either sit it out or, regretfully, run the engine. It is not a motorboat, thank God! And if you run the engine at high power setting it uses a lot of fuel and we have only 40 USGal of it.  The Perkins 4-108 is a very nice engine and maybe the best that was avilable at the time, but with the gearbox it makes for a very heavy weight and the original MD-2 was a good choice IMHO.

Just my two cents of meaningless opinion. 

11 September 2019 - 11:51
#18
Join Date: 02 January 2008
Posts: 1347

Dear Peter

Thank you for the comment, can agree with you that these are basically sailing yachts with auxiliary engines. 
 
For the old models with limited tank capacity it is important to choose an efficient propeller and shaft rpm, and size the engine accordingly.
A guideline is 2 hp/ton displacement, this has been known for a very long time, and is sufficient for calm weather. 
 
If there is a need to power against strong headwinds, this is a more recent matter, but also here calculations should be made towards decent efficiency.
 
For boats with big tanks it appears that propulsion economy has little significance, just put some propeller on the shaft, and make sure there is excessive engine power. Engine dealers are glad to advice. 
Kind regards

 

Lars

14 September 2019 - 18:34
#19
Join Date: 14 May 2017
Posts: 31

Hi Peter and Lars,

Thanks for the clear information. I think I will start with new measurements regarding the suggested requirements. The boat is still in the water, so no problem. Then I think it would be a good idea to use a good and precise RPM meter. Next step might be another gearbox indeed! Hmm..

I will let you know as soon I know more.

Thnx again and kind regards,

Jolling Lodema, Swan 40 #22

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