Alternatives of Engines and the propulsion system - Swan 36 S&S
Hi, Im one of the current owners of the Musiu (swan S&S 36 1969 / # 59), and we are trying to bring this wonderful boat back to life since it sank in last year. We are now exploring options of acquiring a new engine because the boat doesn’t have any, it only has a hydraulic box down the floor tied to the propeller shaft. We still don’t know if this hydraulic box works.

Can anyone guide us on a possible alternative for a new engine and hydraulic propulsion system that suits our boat? Does anyone know if this hydraulic propulsion system can be replaced by another system?


thanks

Jose Ignacio

Dear Jose
Hydraulic propulsion is rare on sailing yachts, but for example Vetus offers installation sets for small engines.
It should be considered that the engine reduction gear is replaced by hydraulic components, and they need to be chosen so the propeller shaft rpm is suitably reduced. For this it is necessary to find out the hydraulic specifications for the present box, and the propeller dimensions.
The installation includes a fairly big oil tank, and the losses in the system are usually considerable, 20% or even more.
One possibility is to remove the hydraulic box, and connect the shaft to an engine with reduction gear as usual.
Kind regards
Lars

Thank you very much for your detailed answer. We have also considered the Vetus alternative since it is a quite a good system given its power of 33hp which is double the power of the boat’s original system.

This reconstruction work seems to be quite long and expensive and, unfortunately, our budget isn’t enough so we had to explore other alternatives. Luckily we were able to rescue the boat’s hydraulic system. This system includes the oil tank and the hydraulic pump F11-110. Looking deeper into this pump, it seems to be built by Parker rather than by Volvo. Therefore, we think we could possibly find out other alternatives to rebuild this boat’s original hydraulic system.

We also found a second hand Volvo Penta 2030 engine used in various Swan 36S&S to replace their md2b 15 hp. Maybe the match between the engine and the pump is easier, we are not sure.

Is there someone who could please guide us on this matching issue? Does anyone have a schematic written guide to match such connections?

Thanks a lot

Jose Ignacio

Dear Jose Ignacio

Oin Stephens' suggested not to install engines with too much power (they are heavy, demand a lot of fuel, and in our kind of boats more than 2/2,5 HP per ton are usless), so think very carefully before getting a so big and powerful engine!

Fair winds!

matteo (38/067 Only You)

Dear Jose
Suggest you find out the propeller pitch and diameter in order to determine its power absorption at various rpms, and the corresponding output required from the hydraulic motor on the shaft. This determines the pump requirements, and the engine power. The help of a hydraulics engineer is recommended.
I would agree with Matteo that the proposed engine is oversized, and suggest you compare the cost of the hydraulic components still needed plus an engine to those of a small engine with reduction gear attached.
Kind regards
Lars

Dear Profesor Lars and Matteo, I really appreciate your valuable comments and recommendations, I made an investigation based on your considerations

1. Power requirement

2. Weight

3. Demand of fuel

4. propeller pitch and diameter

5. alternative about replacing the engine with reduction gear

and this are my conclusions:

1.- the original system has a volvo 15 hp, the new engine has a 29 hp, but the difference in the hp doesn’t make any difference because the hydraulic pump Works with 2300 rpm. The advantage would be that the 29hp would Work easier.

2.- the weight in the Volvo MD2b 15hp is 190 kp (420 Lb) and in the VOLVO MD2030 is 129kp (284,2 lb), the advantage would be that the 29hp is lighter.

3.-the demand of fuel in the MD2b is 2 lts / h and in the volvo MD2030 average is 2 lts/h

4.- propeller pitch and diameter , I don’t Know, but my guess is that it is the original propeller the boat brings, but the difference of hp with the new engine with different hp doesn’t have an impact on the dimensions and performance of the propeller because the pump works with the same 2.300 rpm, and because of that, I think that there shouldn’t be a need to change the propeller. However, we will soon estimate such pitch and diameter.

5.- in regard of the alternative of replacing the hydraulic system with an engine whit reduction gear as usual, seems to be the a much more simple option, but I don’t visualize that because the propeller shaft is located in front of the engine, around 0.5 mts aprox. I have seen a solution in a similar boat, which was to place the engine in the saloon. This boat is an apache which has similar designs (it was designed by Sparkman-Stevens). In the following link (ttp://www.djerickson.com/apache/yanmar.htm) I found out about such adaptation. However, I don’t feel comfortable with this solution.

Thank you, and, as always, if there are other thoughts on this issue, please let us know.

Jose Ignacio