Propping Right a 45 Ft Sailboat.-

[Sea Rider]

My cousin just received a brand new out of the french shipyard Beneteau 45 footer. It's equipped with a Yanmar 40 HP saildrive unit, the lower leg and prop is located somewhere middle to aft of the sailboat. Much better than the traditional shaft and prop drive method. Motor specs states max 3000 wot revs, doesn't state a minimum as in outboards.



The sailboat weights 5 ton bare bone and 6.5 tons with 6 passengers along water and diesel tanks fully filled. As I like to maximize props for top performance will recommended my cousin to go for a wot spin fully loaded on flat calm, no wind water cond and check achieved rpm to check if delivered prop is doing its homework right or so-so.



Dilemma : prop it right for full weight in order to achieve 3000 max rpm or not. Current prop Is a retractable 3 blade prop with unknown pitch factory installed in France. Know that when tanks become empty or with much less passengers or a combo of both situations will need to throttle less for motor no to over rev.

On its maiden voyage went from Callao (Peru) to Salinas (Ecuador) 1170 Km distance in 3 days with sails and motor revving between 2000 to 2500 rpm with excellent low fuel consumption going down the Humbold Current.



Is there someone with proven sailboat experience that can share his personal experience propping right a large sailboat with varying loads.

Happy Boating

 

[Scott Danforth]

My experience has been that if your using the prop more than the big triangle billowing thing above your head...... your doing it wrong. the purpose of a sail boat is to not use the prop other than to get you in and out of the slip

 

[Sea Rider]

Scott,

Seems that sailboats are not your speciality LOL, not mine either but you learn underway when riding on one.

Scenario, you motor the 6.5 ton sailboat out of the slip if counting with one and holly molly there's just a small breeze blowing out there so to move it you must turn motor ON right. You can use any sailboat with motor along sails if wind is unavailable, scarse or wanting a faster displacement speed well over the usual 5-6 knots to around 7-9. Anyway such speeds are very boring ones compared to what an outboard can produce and already used to when going out.

Yanmar recommends to prop it right as will be max loaded in order to run at it max 3K revs on flat calm no wind water cond same as with outboards and throttle less when with less load on board. Need to run it at full hammer down for short time periods in order for the motor to decarbonize itself.

Happy Boating

 

[porscheguy]

FWIW, a 45’ Beneteau whether it’s a “first 45” or an Oceanis 45 actually displaces slightly over 11.5 tons light. Fully provisioned along with passengers I imagine you can get it up to 13-14 tons. And from the data I can find, they’ve got about 55hp.

I would imagine the boat is propped correctly from the shipyard as Beneteau is not new to this business. And people who purchase them are not like people who purchase a new bayliner.

 

[Sea Rider]

I would imagine the boat is propped correctly from the shipyard as Beneteau is not new to this business. And people who purchase them are not like people who purchase a new bayliner.

Yanmar has recommended to make a wot run test on flat calm water cond loaded as will be used and check if current 3 blade prop achieves 3 K rpm. Usually all boats factory delivered with an installed prop are medium pitched ones. Only a wot run will confirm if prop is doing its homework right..

Happy Boating

 

[porscheguy]

Obviously test it out. But I would think that on a boat like that, a medium pitch prop should be appropriate. When you’ve got something whose weight can fluctuate by 5-6000lbs depending on load out, you need to be propped somewhere in the middle.

Another question is does it use a fixed prop or an auto feathering prop? I’ve seen auto feathering props on some rather pedestrian sailboats at the marina. Some of them even change pitch to cope with load and weather conditions.

 

[BillP]

I have not done a sail drive but have re-propped a few large monohull sailboats between 32-42'. Some with volvos and others with perkins. I get the engine torque curve and prop for max rpm at top of the torque curve while tied to the dock. Underway it unloads enough to give you reserve rpm for punching though rough conditions. If you prop for max rpm in calms it may lug the engine when punching though big seas...more so with small vs large engines. Generally speaking I start with the standard calculated size prop (which is usually a best guess but not dialed in for that particular boat) and have it cut down, enlarged or re-pitched. This is way cheaper/faster than buying new props.

 

[Sea Rider]

To prop it right to run towards max 3K wot rpm range will be extremely difficult, one issue is for coastal sailing with medium load and max 6 passenger capacity other fully loaded when cruising at open sea to far away distances. The owner will need to do both tests on flat calm water cond and check which max wot rpm is achieved under both sailing conditions, definitely should dial different max wot rpm ranges.

Happy Boating

 

[BillP]

Like already posted that builder is highly experienced and probably has it dialed in pretty well.

Regardless,..pitching only for 3000 rpm in calms can be had 2 different ways. Small dia/high pitch of large dia/flatter pitch. The smaller will not power though heavy seas as well as the flat lower pitch. Been there on several sailboats and basically I always had 2 props on board for cruising...1 for intercoastal flat water and the other for open ocean and rough conditions. 42' x 24k lb cutter was the last (15 hp Volvo) and there were several before that. Trying to dial in a prop in one fell swoop is fantasy. You can get it close but several trial and error runs get it down to an exact science. This will also show you how over powered today's sailboats are and how inefficient they are running.

 

[Sea Rider]

Thanks for the feed back, but ain't my sailboat. Yanmar's customer service recommended to do the test on both loads. They do agree that prop test are done by very few boaters as most of them are pleased with factory delivered prop.. Same as with outboards.

Personally prefer to mess with outboards props which are more handy, for a saildrive motor will need a diver or a travel lift to take the boat out of the water at an extra expense.

Happy Boating

 

[chris.olson]

Personally prefer to mess with outboards props which are more handy, for a saildrive motor will need a diver or a travel lift to take the boat out of the water at an extra expense.

Anybody with a sailboat in saltwater had better be experienced in diving because cleaning the hull and scraping the prop is an on-going maintenance process.

Full throttle is never used for motor sailing, except for emergency control in heavy seas. It will spend 99% of its life at 2,000 rpm instead of 3,000. It's likely propped for that already. Running WOT when motor sailing is a good way to make sure the tanks are completely empty 200 miles from port, just to gain 2.5kts in speed on your passage on days when the wind doesn't blow.

The engine in a sailboat does not serve the same purpose as an outboard on a planing hull, nor does it work the same. Sailboats have feathering props. No matter what you do, a sail drive is less efficient than a shaft drive. Sure, it gets rid of the maintenance with packing and adjusting a cutlass bearing every time you replace it. But saildrives are for the harbor, marina and docking. Cheap install by the boat builder with a big hole in the boat, passing the cost of running it onto the owner. Nobody that I know of that cruises and does crossings will run a saildrive. So since the boat came with a cheap drive in it, I would suggest taking it at face value and accept it for what it is. It's a day or weekend boat and you're only gonna use it to get the boat in and out of the harbor and slip anyway. WOT performance for motor sailing is a misnomer.