Propeller Advice Needed

[touellette]

Purchased my first sailboat a paceship westwind 24 , I have always been a power boat person under 20 feet , now this is my problem the boat is equiped with a 7.5 Mercury I have been told that the propeller is a reverse ?? which gives more control when backing , however I find its like pushing a barge in forward need more steerage speed in forward , I do not want to go prop shopping until I get some opinions.<br />Tom

 

[mfilleti]

Re: Propeller Advice Needed

Me too! I have a sailboat (22', ~2000lbs, 6hp outboard) and the motor moves the boat forward with ease, but in reverse does almost nothing to bring the boat to a stop or even a slow. I suspected the prop could be changed, but to what, I do not know. Any suggestions?<br /><br />That is all

 

[backdraft]

Re: Propeller Advice Needed

The reason props on modern motors do not work well in reverse is the fact exhaust gases coming out the center [centre for you Canadians] of the prop put many bubbles in the water causing slippage of the prop. In other words the density of the water is compromised by air pockets causing loss of propulsion. Are you near La Salle park on the edge of Aldershot? nevjb

 

[touellette]

Re: Propeller Advice Needed

I live on the Detroit River south of Windsor

 

[Columbia]

Re: Propeller Advice Needed

I've never heard of a propellor being a 'reverse'. Lotsa guys here would know that better. I've pushed a couple of larger sailboats with outboards and they don't slow or stop in reverse as well as you might like but that's because a boat that carries forward well like a sailboat doesn't want to slow down like powerboat with more drag. Changing a prop to improve reverse would be minimally effective. Some boats go to a larger diameter, lesser pitch prop which helps some. Outboard makers have made these kinds of rigs like Evinrude's Yachtwin, etc. But in general, don't approach anything hard like a dock or rocks any faster than you want to hit it.....seamanship, not horsepower, rules here.

 

[touellette]

Re: Propeller Advice Needed

It's my first sail boat just purchassed this year only went out for a short sail with the previous owner one time , after that I was on my own used the just do it learn as you go method , used lots of caution never ran into anything ,moved into the dock as slow as possible , gave myself lots of sea room spent hours tacking back and forth without making headway before figuring what I was doing wrong , Sailing is now a little easier , starting a sailing class with the local power squardon tonight so next year I won't be so green .

 

[Spidybot]

Re: Propeller Advice Needed

It is true. Special props are made for sailboat use where reversing thrust is important at the cost of hi-speed properties. No such prop will ever travel above some 10 mph - instead it should be able to make as much thrust as possible. Merc call it 'High Reverse Thrust propeller' and it has a characteristic blade design: Seen from rear it looks the same as seen from front - the blades have no slant, are almost 100% symetrical and close to no rake at all.

 

[Columbia]

Re: Propeller Advice Needed

Touellette: also be advised that your sailboat will not got faster than hull speed..relatively. It is designed to go about five or six mph unless it's a MacGregor Powersailer. The prop as mentioned above will take more RPM's for a given speed because of the flat pitch. If you want better fuel economy and to run at fewer RPM's get a regular prop or at least one with more pitch than you now have. It's kind of a sliding scale, more pitch equals less power to the water (so to speak)/less control in reverse/more economy and fewer RPM's for a given speed. There's a limit to that. If you want more power, stay with what you have. It's a trade off every time, there's no free lunch.

 

[touellette]

Re: Propeller Advice Needed

I won't know how much forward motion the prop provides as I have only sailed / motored in Georgian Bay no current , I trucked the boat home this month , next year will be a now game as the current in the Detroit river can be from 4 to 6 knots depending on location so long as I can make reasonable headway with good stearage I'll be a happy sailor if not I may be looking to trade my 7.5 merc for more power

 

[Columbia]

Re: Propeller Advice Needed

More horsepower will not necessarily get more speed out of your boat. It'll only go so fast through the water. The pic of my old Freedom 25 above is powered by a 6hp Suzuki and it would power us through 20 plus kts of wind on the Columbia River. Once underway, windage is the main limitation for horsepower in a sailboat kicker with your boat size/style and motor size. Your boat will only go so fast and no more. That said, you can squeeze a couple mph more speed out of a displacement hull by applying lots of extra power but even then it is quite limited. My rule of thumb when sailing in river waters with a current is..always sail upstream first, then you can get back if the wind fails or the current is too extreme. Good luck!

 

[touellette]

Re: Propeller Advice Needed

Oh for sure sail up stream first and mother nature is on my side as the prevailing wind's are from the south / west which in my case means I will / should be able to sail both ways and in the worse case the current will take me home just have to avoid the heavy shipping , Oh by the way I see your from Oregon my wife's brother lives just outside Portland just met up with him for the first time in a few years last week at his daughter's wedding in Toronto , haden't seen him since I dropped in on my way back from visiting my son in Vancover

 

[mfilleti]

Re: Propeller Advice Needed

Wow! Lots of great quick response here. <br /><br />I understand now that reverse will never be as reliable as forward. And I like the idea of getting the high reverse thrust prop that UU spoke of.<br /><br />Before I rush off and get a new prop to replace my prop; is there such a place that lets you try different props before you buy? My current prop is just a plastic thing and I suspect it magnifies the ineffectness of reverse. Perhaps a regular alum prop would be just fine?<br /><br />Another question about the high reverse prop. Would I have a hard time motoring against waves and wind with such a prop? Would the poor forward thrust be such a hinderance that it would out-weigh hte benefit of the improved reverse response? Remember I mostly use the motor to get on / off the dock, and putt home when the wind dies. Forward speed and thrust don't seem that important to me except for beating over the waves and wind during a storm or bad weather.<br /><br />Thanks again for the response<br />Matt<br />T.O. Canada

 

[Columbia]

Re: Propeller Advice Needed

This is one of those issues that is of the 'depends on what you want' school. I personally wouldn't sacrifice good forward speed and economy for better reverse. I hardly ever use reverse and just go slow toward hard objects often putting the engine in neutral 50' before my slip. The boat's forward way carries me in. When I back up I've found that just letting it idle out of the slip is better than trying to 'give it the gas'. Due to a cross current exit from my slip where I want to back upstream I'd pull the boat out manually 'til I have the right trajectory, climb aboard, put'er in reverse and head back. Remember that you have the propellor turning one direction creating 'propwash' and it tends to move the stern to that side in reverse. That's why I back out manually in neutral, the propwash throws the stern to the downstream and I have to back out toward the upstream, turning the boat a bit manually, or back all the way out of the marina. Backing out of the marina is too exciting to do very often.... Once you have some way on in reverse, the propwash is not so important and the rudder will direct you successfully...but you have to have some way on.

 

[Curzon]

Re: Propeller Advice Needed

I have to concur with Old Sailor on this matter. You are best not trading off forward thrust for reverse ... it never equates. Sail your vessel as if you have no reverse thrust and you will do ok. This requires a little Situational Awareness and a great deal of prior preparation and planning. I came off an Australian Volunteer Coast Guard SharkCat with twin 200HP Yamahas on the transom ... and went to my Hartley TS16 trailer sailer with no reverse thrust at all ... it soon made me aware of how rusty my seamanship skills had become. A little dedicated practice, using a mooring buoy as an aiming point, and the skills soon returned. In fact there is nothing in the world so satisfying as coming up to a dock, cutting the power at exactly the right moment, putting the helm over and gently drifting alongside with barely a whisper of a nudge. Trust me, you can do it everytime if you put your mind to it, no matter what the conditions.<br />Re the prop trade off though, you are better keeping the optimum forward thrust prop for your hull configuration ... it will assist you in getting out of difficulties in heavy weather ... hopefully!<br />I really love this site ... you guys are all so knowledgable!

 

[Spidybot]

Re: Propeller Advice Needed

As mentioned, a sailboat (unless special design) will only move so fast (waterline lenght in metres equals speed in knots). A 20' is 6 metres and will do approx 6 knots (speed through water - not over ground). No matter the size of motor or sail, this a rule. Going against 6 knot current at full throttle will, in practise, make you sit on the spot.<br /><br />This is completely different from planing hulls (powerboats or planing sailboats) and goes for all displacements hulls (sail or power).

 

[touellette]

Re: Propeller Advice Needed

In this case I've lucked out , with no wind I should be able to maintain around 3 knots going against and with the prevailing winds move at max hull speed , now going with the current does the speed pick up with a trailing wind ?? lets say the current is running at 4 knots and the wind is at 10 knots would my hull speed increase ?

 

[Spidybot]

Re: Propeller Advice Needed

Speed is defined in two ways: Speed over ground and speed in water.<br /><br />If the current is 4 knots and you're 'sailing' with it you'll make 4 knots over ground and zero knots in relation to the sorrounding water. By going 6 knots measured in water you'll make 10 over the ground.<br /><br />A paddlewheel log will tell the hull speed in water, a GPS will tell the speed over the ground.

 

[Columbia]

Re: Propeller Advice Needed

Toullette: I'm a mite confused what you said last post but..If you only can power at 3 knts forward you will be at a severe disadvantage if you have to go against any current. If current is one, two knts, you will go soooo slowly, if 3 knts, you will move upstream not at all. If more than that, as you suggested you experience currents faster than that, you will be going downstream backwards. As a guy who sailed wind and tide and ten foot oars for ten years on the lower Columbia River...wind ain't reliable. Don't count on it against the current. If you sail in a river with current, I reiterate that you NOT sacrifice forward speed for reverse power. The hull speed of your vessel is essentially fixed by design and does not increase or decrease as a result of conditions you boat in.

 

[touellette]

Re: Propeller Advice Needed

OLD SAILOR :<br />What I was trying to say is that my estimated speed is in the neighbourhood of 6-7 knots using the motor only in still water and the current in the Detroit River is anywhere from 4-6 depending on location . How would I find the design hull speed of my boat ?? Any way I will find out on my first outing next spring as the channel where I will enter the river system is narrow and the current is at it's max , I have rowed and power boated this area for close to fourty years just never in a sail boat

 

[Columbia]

Re: Propeller Advice Needed

I saw your ads for crew. How did that work out or did you ship? I think you've overestimated your hull speed but I don't know what your underbody looks like. What type of keel do you have? Ordinarily, the tradional formula for hull speed of a displacement hull is 1.34 times the square root of the LWL. If your waterline is 20', then the square root LWL is 4.5, times 1.34 is 5.9. Thus the theoretical hull speed is a mite less than 6 knts. That formula is an attempt to find hull speed but it is more complicated than that and I would frankly be surprised if it was that fast. A lot depends on your underwater lines. I've owned bigger sailboats than that with longer waterlines than that and no more speed. I'd expect five knts tops. River sailing without the benefit of a tidal range is often frustrating because when you're 'ripping' along and tacking upstream into the wind you can find yourself making zero headway as all way made good on a tack can be eaten by the current pushing you back down. A four knt current can eat your max hull speed easily so no distance made good over the ground. What kind of winds do you get there? The pic is me in '80 on my old Benford 22. I modified the rig to a stays'l sloop for the high winds we get in the tidal Columbia River area. The pic shows winds to over 30 so I'm double reefed main, stays'l only. Not much fetch to build waves there. <br />