A4 Owners: RPM Table

[Sea Haven]

Shipmates, specifically afourians.....

As my rig still needed the Spartite installation and subsequent tuning, we decided this past weekend to continue drive train and Engine testing. Beth and I generated "initial" RPM Table. It was done at high tide slack before EBB, Wind out of the NNW 11-15 kts  (just abaft/before the beam) heading due west and then due east. All within Mount Sinai Harbor. FWIW it seams like my aftermarket RPM Gauge, which is hooked to the coil, is a bit "jumpy" so it was difficult to gauge the exact RPM, so I had to average those too. The speed is SOG, measured with a Magellan handheld GPS indicating an EPE of 15'. Averaged with in each leg for a given RPM, then those were averaged on the opposing legs. 
Though it was possible now to achieve 3K RPM, which is a first for me on this boat. Last season one of the many new owner "teething" issues I had were the valves on cylinder three  appeared  to be stuck as evidenced by low compression. They "miraculously" started functioning for me after the addition of MMO to the gas at the end of last season and it's like I have a whole new engine now! Before she wouldn't go above 2.2K rpm. This is only my second season with her and I'm still learning her as well as working out bugs left from the PO. I did not like to hold it at 3k  for long as she would smoke (unburned fuel). She really seems to like the 1.8-2.0K range, but I believe 2.0-2.2K might be the optimal cruising RPM, as mentioned by DOLCE VITA in other threads here. Many thanks to Ed on a phone call that helped troubleshoot this.

The following is the initial RPM Table, more data will be gathered over time. I also want to work more with the upper range (baby steps here!)
Plotted the curve here in EXCEL and it's kind of "off", not a smooth power curve like I expected. Again, more data needs to be gathered.

Hopefully one of those "dead" calm days where the water looks more like "oil" than water!

Ed of Dolce Vita, I'd be interested in seeing your numbers as we have similar configurations in drive train.

RPM   Avg Speed (kts)

1000     2.8

1200     3.3

1400    3.6

1600    3.7

1800     4.0

2000    4.7

2200    4.9

2400    5.5



FWIW, we did install the Spartite, good stuff!!
Now it's time to develop a polar sail chart!

"Sub" Ed

[Dolce_Vita]

Ed,

  Thanks for all the kind words.  Glad you're running well and your compression numbers came back up.

  I'm on travel to NM right now, but I'll try to gather some similar numbers the next time I have the chance.

  Meanwhile, from memory, with a freshly cleaned botton & prop, in calm flat, I do somewhere around 5.0-5.2 kts @ 2000 rpm. 

  The condition of the prop makes a HUGE difference!  Prior to cleaning, I had only about a dozen barnacles on the prop, but it brought my speed @ 2000 rpm down by a full knot!

  I forget what prop you have.  Mine is a 3-blade 15-8.  I'm thinking of getting it repitched up to 15-9 next year, as I can't drive the boat to hull speed even at 3100 rpm.

[Sea Haven]

Ed,

Though the surveyor listed my prop as 16x8, I went and too a gooooood look it after reviewing several of your discussions here.

Lo and behold! It measures 15" (7 1/2" to blade tip from center, annnnnnd (drum roll please!).....its marked 15x8!)
I'll save my opinion of my boat survey for another day.

So I think we're close to identical.

FWIW, I just read on the work order for Shaft replacement and PSS Dripless Seal installation, he reconditioned my prop as well 
Like I said......grinning ear to ear!

I am looking at the possibility of a Gori feathering prop, even having a conversation with a salesman now, here's part of it concerning selection.......

Hi Ed,
 
From the photo of your existing 15” dia. propeller you have plenty of room for the optimum 16.5” dia.
Typical tip clearance is 10% of dia.
 
If clearance is an issue & as tip clearance is also important we can work with you in optimising the diameter & pitch for your installation.
If you need to step down in dia. size let us start with the actual clearances so that we can optimise the propeller.
The folding propeller "sits" further aft on the shaft than does a fixed prop.
 
Quite often with shaft down angle & hull rise you can gain more distance the further aft you measure on the shaft vs. straight above the shaft taper.  Can you supply the distance from the shaft centerline, measured at right angles to the shaft centerline at the end of the shaft thread (aft end of thread), up to the hull?
 
As a larger dia. gives a greater efficiency, i.e. absorbs & puts out all the hp & puts it out as thrust it will pay to go with the largest dia. possible.
 
Yes AB Marine will be at the Newport Boat Show – we can show you the features & benefits of the Gori.
If you are planning on extended cruising then you should seriously look at the 3-blade also.
 
From your engine hp & boat size ( I don’t know your cruising/sailing style description, i.e. extended cruising) I would definitely go with a 3-blade folding propeller over a 2-blade - giving you the best of all worlds for performance sailing, club racing, motor sailing or motoring.
 
A 3-bladed propeller has a greater BAR(blade area ratio) than a 2-blade propeller and therefore develops more thrust(power) at any rpms.  The boat will accelerate quicker / stop faster & more importantly, punch thru waves in a head sea/head wind/against the current a lot better - maintaining boat speed, not slowing.  With an engine of 25hp or more, a 2-blade propeller does not have enough blade area to fully use the hp available in the engine room and put it out as thrust into the water.
 
It is now possible for you to have the folding propeller's speed advantage under sail, with the thrust similar to or better than that of a fixed propeller when motoring and definitely motor sailing and near zero drag when sailing.

A Gori 3-blade folding propeller gives you:

More thrust & power - especially when power is needed - as in adverse conditions, heavy seas, against the current or emergency manoeuvring - due to the 3-blades which have an higher blade area ratio than a 2-blade or other feathering or folding propellers.
 
Full thrust / full power in reverse & no prop walk in reverse due to the unique reversing folding action which allows for the identical leading edge as in forward. It is the full weight and centrifugal force of the blades being opened, whereas a feather blade is only rotating and there is little inertia from the actual blade itself.
 
Higher efficiency (more power/higher boat speed) at lower rpm settings & throughout the rpm range because of the True blade shape (camber, rake & curve)

Increased thrust & speed for motor sailing resulting in less engine noise, vibration & increased fuel economy, greater cruising range when using the overdrive function which allows for an increased pitch over normal (of 2-3").
 
Lowest drag possible of any fixed, feathering or folding propeller(whether 2 or 3-blade) giving increased sailing speeds & less rudder turbulence, higher pointing & better steerage when sailing as the geared blade design ensures that all three blades open & close together. The 3-blade is std on most big race boats & performance cruiser racers.
 
Till then, any questions that the admiral may have just call or email.
Best regards,
 
Geoff Prior
AB Marine, Inc

A bit pricey, but I am considering it since I don't plan to sell....ever!

Regardless, establishing an RPM table baseline not only helps us in voyage planning, but should help in flagging potential issues before they occur, like said barnacles lol.
I need things written down lol!!

I do have to ask, I get a bit nervous staying above 2400 RPM for sustained periods as I don't want to "red" line her. Am I being too nervous? Like I said she seems to smoke (dark) when I peg it (pushing 3100 RPM) . At cruising RPM (2100) NO smoke/steam at all!

"Sub" Ed

[Alma]

Be sure to look at the KIWI Prop too. I hear great things about the composite feathering propellor.

[Dolce_Vita]

I do have to ask, I get a bit nervous staying above 2400 RPM for sustained periods as I don't want to "red" line her. Am I being too nervous? Like I said she seems to smoke (dark) when I peg it (pushing 3100 RPM) . At cruising RPM (2100) NO smoke/steam at all!

"Sub" Ed

I don't think you have to worry about "red-lining" her.  The max rpm is listed as 3500, and I don't think you could ever get her that high while spinning a prop in the water, so I wouldn't worry about damage from over-reving.  Of more concern is that I find that my oil consumption goes up drastically above 2400.  In my case, I don't notice any smoke, but the oil goes somewhere!  I learned this the hard way by pushing into chop and headwind at 2600-2700 for over 7 hours.  My oil level got so low that when the boat rolled on the swells, the oil pressure would momentarily drop as the pickup in the sump became uncovered!  Below 2200 I have essentially zero oil consumption.

If your smoke is gray or dark, it may be from an over-rich mixture rather than from burning oil.  Oil smoke is bluish-white and persists.   Steam is white, but quickly dissipates. 

An adjustable main jet is an easy add-on and allows you to tweak your mixture at cruise rpms.  This has the added bonus of improving your gas mileage.  When I got mine tuned up, I went from about 1.25 gal/hr to 0.75 gal/hr, and my plugs stopped fouling.

[Sea Haven]

Ed,
Thanks for the assurance, and I'll keep my eye on the oil consumption too. The smoke I saw was definitely not oil or steam. I bought the adjustable main jet last year when I purchased the rebuild kit. Now that I have the other "issues" resolved, I'll start "tweaking" it as you suggested. I'll have to compute the fuel flow rate manually for now.

Alma,
Do you have the KIWI prop?

Thanks!
"Sub" Ed

[Alma]

Yes an adjustable main jet is key. The fixed jet was designed for the good fuel available 40 years ago!

There is also a carburetor housing mating surface upgrade on Moyer's site that I performed over the winter. The procedure addresses too lean a mixture at certain throttle settings. It is about filing the castings to insure they seal against the body gasket correctly. Check it out but go easy- it can ruin the body to remove too much material.

I have my main jet turned in so close to lean I see a need to use the choke in the Summer when starting up cold. With the old fixed jet I only needed the choke in freezing weather. I now use the choke to start in summer then push it in after a few seconds. I also noticed a big increase in "milage" too with the lean burning adjustable jet.

It isn't possible to get the same detailed tuning information we used to with spark plug visual charts with our modern fuel. The best we can do is note that all are the same and not sooty. I'm also running Pertronix ignition and that helps economy and smoothness too.

A friend who had some antique cars told me all flathead engines (like the atomic 4) consume more oil than we are used to. I know my old 4 can burn a lot of oil if I push it and I do see some oil smoke mixed with steam when the water is very cold but I also add an ounce / 5 gallons of Marvel Mystery Oil which might show smoke.  It keeps the whole engine from fuel tank to exhaust nice and clean.



Most important is prop fouling. I can tell when mine is fouled- everything vibrates- lazzarette hasps, ladder, engine cover, stove-



And after that little Great White was filmed near where we sail last week I've got the Heebe-Jeebes about lingering under the boat scraping my propellor!

[Sea Haven]

All Shipmates regardless of iron genny,

The HOW and WHY you should take the time to do this:

How to Make an RPM Speed-Table for Your Sailboat

"Sub" Ed