Prop Sizing for a 43' DC

[Triskele]

I am wanting to pick up a spare set of props for a 1981 43' DC. According to Hatteras, original equipment was 24 (dia) x 24 (pitch), 1 3/4 shaft. A recent marine survey lists them as 24 x 22. Have not been able to confirm so not really sure which is on there. My question is...can a left prop be turned around and used as right and vice versa or do I need to buy separate props for each shaft? Next to the shaft size on the marine survey was "SS" which I presume stands for straight shaft as opposed to tapered.

Another question...does prop sizing effect the manuverability of a boat in port? I live aboard and the boat is loaded down. Although I can't really get her to plain off because of all of my crap on board, that is not such a concern to me. I would like her to be more responsive when steering with the props on idol. I'm sure experienced captains will think I'm nuts for asking this question, but I am in tight quarters and would want to switch over to a prop where I would give up some control in steering. Just a consideration.

Does anyone know the largest diameter prop I can run on this boat? In terms of choosing a prop (and again I realize there will always be the qualifying "it depends") for the purpose of fuel economywhich is better...small or large diameter? How about pitch? How does it work with or against diameter? Can anyone send me to a site that will explain the meaning of pitch and how it is derived and the trade offs between pitch and diameter? I would like to know what the difference is between a prop with a 22 pitch vs 24 or 26, etc. etc. How do the different pitches effect performance?

For instance, can anyone tell me how a 23 x 26 prop would work on my boat vs a 24 x 22? By the way, if it matters, I have JT 6-71Ts.

Have looked over discussions on other forums on props. Lots of information, but a little difficult for a novice like me to piece it all together...especially with the use of boating jargon and abbreviated discussions more suited to the experienced. Any advice is greatly appreciated. Thanks!

 

[Avenger]

Propping is part science, part black art. I can't help you with the specifics of your boat and props, but I can answer your first two questions. No, you can't reverse a prop. And SS means stainless steel.

 

[micky]

The original ones are supposed to be 24 x 24. A couple of month ago I bought the same boat and someone played with the props before and when I put the boat in gear it didn't move, as if it was in neutral. I took the props to the prop shop and they made them 24 x 24 and the difference is HUGE. Now she responds like a boat should respond. I asked here for the size before doing them and everyone recommended 24 x 24. If you add too much pitch you will overload the engines. And you need a RH and a LH prop.

 

[rwappleton]

I too have the same boat with J&T 6-71 TI's 390HP and mine has 24X23's. With a less than clean but not terrible bottom she did 21KTS on sea trials with full fuel and water. She cruises well but exact fuel specifics are not nailed down yet. She also handles well in close quarters.

When we leave the yard and I find out what hull speed is we are going to do some fuel GPH at hull speed testing as well as specific rpm's for our loop trip.

I have been around boats most of my life and I have always been told put on the biggest that will fit and adjust with pitch. when I look under the boat it appears that bigger props and the water flow would go around (read over and under) the rudder adding to the lack of handling. Mine seems to be perfect and I'm not going to mess with it.

 

[dsharp]

A general rule of thumb is an inch of diameter = 2" of pitch. So your 23x26 is equivalent to a 24x24. If you go to Michigan propeller they have some info regarding clearance from the hull, etc. For a heavy vessel that takes some umph to get it moving you want to get as much diameter as you can within reason. The other main factor in wheel selection is vessel weight. The factory recs are fine when the boat is new but it's not uncommon at all to take an inch or two of pitch out to take some load off the engine and let it turn up its rated rpm. Too much prop is the same as running your car down the road with your foot on the brakes. Before you order a set of spares you need to take the boat and run it with clean wheels and bottom, full of fuel and water and see if the engines will reach their rated rpm. Another general rule of thumb is you pick up 200-250 rpm for each inch of pitch you take out. Before anyone starts screaming that's just a general approx. based on my experience with Hatts in the 36 to 46' range.

 

[saltshaker]

Most likely the surveyor wrote down what's stamped on the props. Unless the surveyor actually measured the props, you won't know for certain what you have until you bring them to a prop shop. If your boat performs well and she reaches max full load RPM, stick with what you have. If performance and or WOT rpm is not what it should be, write down some performance, rpm figures and take the wheels to a good shop. They'll be able to tell you what should achieve ideal performance. Before you do any of this, you want to make sure the engines are hitting rated no load RPM. If not, you need to figure out why before you can do anything with the props.

 

[jim rosenthal]

You need a minimum clearance between the propeller blade tips and the boat bottom, for several reasons. One of them is enough room for things not to get caught in there. I think it is ten percent of the prop diameter, but I'm not certain.

Generally the factory sizing is pretty accurate assuming a clean bottom, healthy motors, and a well-aligned shaft system without a lot of friction in it. And props that are properly sized and tuned. Modern prop shops are able to do a lot more than they were back when most of our boats were made- computer measuring etc.

Prop sizing does somewhat affect low-speed handling, in the sense that if you add pitch the boat will respond a bit faster at low speeds, but you will overload the engines at top revs. Your props should be sized to match WOT and permit the engines to get to rated speed. You also have a heavy boat, by your own account- your props should have LESS pitch, if anything, not more. Your boat is likely to be above her design weight. And low speed handling is affected by other things as well, that you can't change, like rudder size, for example.

What I would suggest is to get your present wheels tuned and pitched for best all-around performance. Once you have done that and you are satisfied with the results, then look for a set of spare wheels in that size. Tuning your boat also involves making sure the shafts are aligned properly, the cutlass bearings are in good shape, there is minimal friction in the drivelines, and that your cable control systems are allowing the engines to reach full revs under load. I think verifying all those things is a better use of your time and money than shopping for spare wheels- and adding spare wheels means even more weight to haul around.

 

[TROUBLE]

I have a 1972 43 dcmy with 8-53 naturals. I run 24x24's and they seem to be perfect. At 1200 rpm i am running 8 kts, at 1500 rpms i am running 9.5 knots and my wide open throttle is in line with my motor specs ie: speed and rpm

Art

 

[DBYS]

Deep Blue Yacht Supply does free propeller sizings. The link to fill out the sizing form is on the home page.

Mike

 

[DBYS]

Here is the link, http://www.deepblueyachtsupply.com/propeller-sizing

 

[Jaxfishgyd]

Yup.... Mine are 24X24