Steerable Prop on a coastal trawler

I want to relook at what might be possible to design a simply 'steerable prop' for a coastal single-engined displacement trawler in the 30'-50' size range.

We all know the superior maneuverability of twin engine installations, but can we achieve this sort of maneuverability with a single-engined boat?

You might ask what prompted this desire to investigate such a matter? Long ago I imported a 37' sailing catamaran from France. I began to explore how to power it when not sailing, and I chose to look at outboards. At the time Yamaha was introducing a new special 9.9 hi-thrust model. It developed its hi-thrust by having a lower gearing ratio in its drive train, and turning a bigger dia prop. It pushed that that 37 cat at about 7 knots in calm water,..wow.

Next I looked at maneuverability. I found that I could attach lines to my rudder arms such that I could steer that motor when docking. I could "Parallel Park' that vessel like one would do with a car. It amazed a lot of folks !....my slow backing capabilities were fantastic.
Weekender/Picnic Vessel, Power and/or Sailing Catamaran https://www.boatdesign.net/threads/weekender-picnic-vessel-power-and-or-sailing-catamaran.33751/page-4#post-873087

 

Many of the 'pod' type systems utilize some form of hydraulics or mechanic shafting to transmit the engine power down to the prop shaft. I believe there is a more efficient, and simpler arrangement, its an old time technology know as 'silent chains' . Have a little look here if you are unaware of them,... Ramsey Products | Silent Chains For Power Transmission https://ramseychain.com/products/power-transmission-chains/

Quite a number of years ago, PYI made use of them in an outdrive leg,..





Can you imagine something like this as a rotatable drive leg?

 

Hi Brian, it may have a fancy name but it's still just a chain, it will work if set up correctly. If the seals always keep everything nasty out of the oil bath. The tricky part is getting the power to the leg's input shaft(s) while allowing it to rotate, so hydraulics is still a useful concept. Or an electric motor + g/box mounted over the leg, driven by a diesel electric generator. Mitre / bevel gears may still be needed in the drive train if a large ICE is used without hydraulic or electric power transmission.

 

The OXE diesel outboards do it with heavy-duty belts: https://images.marinelink.com/images/maritime/-104202.png

 

I would suggest you do a little more reading about those 'silent chains',...they are more than just a chain.

That might be a real possibility, particularly with the reduced size of some of those very modern electric motor designs. And with electric motor propulsion there may not be a need for the tradition gearbox,...AND switching prop/motor rotation/direction can occur very quickly.

 

Not as much participation in these discussions on this forum, BUT I would suggest looking thru these 2 subject threads over on the Trawler forum,..

Perhaps I need to abandon this more complicated idea of a steerable prop,...and spend more time on the Becker flap rudder concept. It sure seems to make sense. Makes me wonder why we have not seen more applications on our trawlers these days.

VERY interesting discussions !. over on this subject thread,..
rudder extension??
In a boat listing picture I can see someone welded an extension on the back of the rudder. I would guess this was to provide more steering by increasing surface area. But out of all the models of this boat no one else has done it. Could this be a warning of something to be aware of?
www.trawlerforum.com


It makes me wonder why there has not been more use of the Becker types on our trawlers ??

 

No, the powering and sealing of the rotating leg with that bolted to it would be a nightmare. That is why rotating drives powered by mechanical systems have vertical drive shafts.
I suggest you study log broncs.
https://www.reddit.com/r/loggers/comments/196r8ef/log_bronc_boom_boat/

 

I have abandoned this idea of a steerable prop after being sold on the simple idea of an articulated rudder type,...a Becker 'flap rudder type' discussed over on that trawler forum.

...much simpler, and much less expensive to incorporate to attain extra maneuverability, both at hull speeds and slow docking speeds

Discussed briefly here on this forum:
Becker Type Rudders https://www.boatdesign.net/threads/becker-type-rudders.9889/#post-70442

an excerpted posting there

 

Relatively simple installation here,...


might be future reduced in simplicity...?

 

This would work nicely, especially if there were a clutch to disengage the main propeller.

 

Why would I want to be dragging all that extra prop/gear around?...that could really slow our boat down, and require even more power to attain hull speed.

 

Products | Becker Flap Rudder https://becker-marine-systems.com/products/manoeuvring-systems/becker-flap-rudder

 

Outfit in our local made what they call a deflector rudder, same idea but a bit stouter mechanism. They were all the rage about 10 or 15 years ago as we have shallow tunnel hulls being applied to fisheries that need maneuverability. A very emphatic friend installed one and we took in through its paces. My then boat was his direct sister ship and it was most pronounced in it's capacity in reverse, a weak point on our hulls especially when light. It did pivot more on static turns, but having installed a bowthruster my hull could also pivot rapidly static. At the time my hydraulic thruster was actually a cheaper install than the deflector although my guess is they have both gone up in price and are closer to parity in cost.

On my new build a few years back we went thruster and a plane Jane foil shaped rudder, when manipulating nets my preference is thruster at the bow as a rudder still needs my prop engaged under our hauling area to work.

They do seem to work pretty well, can think of several with a decade of commercial use. Would think a diy one would make sense if you have the tools and the skill. Friend is doing a refurb of a boat to see him to retirement, he opted for a deflector and jokes hes taking it with him when he retires. It was a tad over 8x more than his quote for a standard fabbed 316 rudder. Will be a heck of a mailbox mount or yard art.....

 

yes, in work with nets, I would think the flap rudder would be at a disadvantage

 

It does not appear to be a constant velocity joint, so the vibration when not colinear would be significant. They are not counter rotating so that the effectiveness of the second prop
would be seriously impacted