Yanmar3GM30 and Maxprop

BCC Forum
1

Before buying Itchen I spent a lot of time cruising on a friend’s Victoria 34, which has similar displacement, and the identical Yanmar 3GM30F and three-blade MaxProp combination. On the Victoria, with the Maxprop pitch set correctly after much experimentation (16, I believe), the boat reached cruising speed around 2800 rpm and max hull speed somewhere between 3000 - 3200 RPM. With Itchen at the present MaxProp pitch setting, maximum hull speed is reached at about 2100 RPM and she cruises comfortably a 6 knots or a little less (depending on conditions) at about 1900 - 2000 RPM.

Fussing with MaxProp pitch settings takes some time & hauling expense so here’s my question. What MaxProp settings have others found to work for a BCC with the 3GM30 and what RPM’s for normal cruising & top “flank speed”? Based on Yanmar’s engine specifications, Itchen’s 2000 RPM seems very low and inefficiently placed on the 3GM30’s RPM/horsepower curve. On the other hand, the engine sounds happy enough, fuel consumption seems normal and there’s no black smoke when pushing at max rpms.

Itchen is now in Charleston at the City Marina, where I left her last week on one of several legs of a Bahamas-bound cruise. Dottie and I will pick her up and continue towards Florida later this week and chances-are that I will haul her for some routine zinc replacement and Maxprop lubrication once we get to Florida – so that would be a chance to do some MaxProp pitch adjustment, if anyone has a recommendation.

2

Scott,

We have the Max-prop on Galatea, and hauled her 3 times to get it set right. I don’t have the figures with me, but I seem to remember that I replied to a question on this once before, so you might check the archives. We can run the engine out to 3600 rpm, and get hull speed (with a clean bottom) at about 3200 rpm. We get alot of propwash that shakes the Freehand trimtab, so I generally limit our motoring speed to 5.5 knots or so.

Hope this helps.

Tom
SV Galatea

3

Tom,
Thanks. That is helpful – and unfortunately, what I suspected. Since the present pitch setting at least works, I think I will be conservative and try setting the prop one increment finer next time she’s hauled. At 2000 RPM a lot of horsepower is not available. On the Victoria 34 a setting only one increment too high or too low made a big difference. When set too coarse she would pull like a tugboat in reverse but stall in forward! One season she was launched with too fine a setting and had a top speed of only 4.5 knots!

The specifications notebook for Itchen is on the boat so I’m not sure what the present setting is but will know in two days when we get to Charleston. I just did some searching in the old Yahoo BCC archives and noticed that Itchen’s setting in 2003 was said to give hull speed at around 2400 rpm. I think she should do better with a finer pitch setting. After a day spent doing a RPM/speed graph, 16 degrees of pitch was optimal for the Victoria 34, which had similar waterline & displacement but less wetted surface than a BCC. I believe 16 degrees has been mentioned as a successsful setting. Does anyone know if all the BCC’s with Yanmar 3GM30’s have the same gearbox ratio? Itchen is #73, 1985.

4

From memory, Tom (and other BCC owners experimenting with MaxProps) had found that the 16" three bladed Max Prop was optimally set to 16 degrees, 8.6 inches of pitch, and letter settings of X = C; and Y = K.

I had explored fitting a MaxProp to Zygote, but got cold feet after learning that owners of other boats (ie not BCC28s) with Yanmar 3GM30F engines and Kanzaki transmissions discovered that the Kanzaki transmissions were damaged by the transient impulse when their MaxProps opened.

Tom and Jill have shown with Galatea that the MaxProp delivers an extra 1 knot or so of sailing speed, excellent reverse handling, and good ability to stop the boat. Whether the MaxProp is really incompatible with the Kanzaki transmission remains to be seen.

Cheers

Bil

5

It is possible to change the pitch without hauling out - I did it many times on BCC #4. I have no idea what the maxprop settings were since it was 10 years ago. This is, of course, not recommended. Anyone who tries this must be either mad or out cruising.

You will need ropes, safety lines, a no-hub coupler (for sewer lines) with cap, a mallett, a dinghy, the ability to work in a confined space almost inverted, and lots of patience. I do not know if it works with those modern dripless shaft seals, but I’m sure anything is possible.

  1. unbolt shaft from transmission

  2. remove shaft coupler from shaft (requires aforementioned mallett). This requires brute force and ignorance.

  3. unship rudder using topping lift - don’t worry, it floats - and float it out of the way. You may not need to do this - my maxprop would not quite clear the rudder aperture. Try it with the helm hard over first.

  4. push the shaft out about a foot.

  5. secure safety line to prop and shaft to prevent loss of both. Suggest a shallow anchorage for your first try. Use dingy, get wet.

  6. push the shaft out until only about an inch remains inside. The prop end of the shaft is now supported by the safety line.

  7. remove shaft packing nut - water will enter boat, but slowly because there is very little clearance around the shaft.

  8. secure capped no-hub coupler to threads where you just removed packing nut

  9. tighten securely with 2 hose clamps - water intrusion will stop.

  10. get in the dinghy, go to the stern, reach waaaaaay down (you will get a bit wet) and pull out the prop and shaft. May want to load all heavy gear forward to put the bow down. My first try involved anchors, lead ballast bars, the unshipped rudder, a small crowd, and a water-filled dingy on the foredeck. This is not needed as long as you don’t mind having a wet face for 5 seconds. Otherwise, you can almost get the prop out of the water.

  11. make adjustments, repack with grease, and reinstall. It takes a great deal of patience to re-ship the rudder, since its flotation fights you. But, when you are cruising, every day is Saturday, and you really don’t have anything else to do anyway.

  12. enjoy the number of binoculars pointed your way as everyone in the anchorage tries to figure out how you did it without sinking.

This is a useful procedure for many reasons: pitch adjustment, cutlass replacement, removal of your own taffrail log line from the stern tube after backing over it, etc.

There is also something to be considered re: transmission wear. I killed a small Hurth gearbox (junk - never have one) in under 10 hours of run time before upgrading to a larger model than recommended. Long term, I fear that was even too small. Don’t fool around with your machinery - get top notch, continuous duty hardware. So many mistakes…

In retrospect, I may also have angled the motor a bit to reduce the helm when under power. This may not have helped due to the keel/motor alignment (look at your engine pan to see this approx. 2-inch side-to-side difference due to the hull mold). Unfortunately, once cast in several feet of resin, there’s no moving the stern tube to try it out.

Just my experience from a long time ago - your actual mileage may vary. I never came close to sending my prop and shaft to the bottom - the balance point was prop up, engine side down. When you are away from marinas, you find a way. Please don’t call asking me to retrieve your prop and shaft from the bottom of the bay, where it now sits happily under the layer of hats, sunglasses, and winch handles.

Respectfully,

Todd Chocholaty
ex-hull #4

6

The Yanmar 3GM30F originally came with a Hurth/Kanzaki transmissions KM3P 2.61:1 transmission, rated for a slightly larger engine than the 27hp supplied, recent trend from local distributor is to supply replacement with the KM2P, lower rated transmission. Both transmissions have a large reinforced aluminum front transmission cover/keyhole adapter; with a fixed bladed propeller and treated with a healthy respect for avoiding high speed shift changes, these transmissions have held up reasonably well.

However, neither transmissions respond well long-term with folding/feathering propellers which load up suddenly; end result is distortion of bearing recess in the front cover, the press-fit bearing race spins, causing premature cover bearing recess wear, generating heat, bearing misalignment, excess input shaft end play and a real nasty howling sound. In severe cases, the transmission locked up into a pile of scrap metal.

We replaced 3 of these KM3P transmissions in one year on three different boats of course, no reason to create panic here, most have gone many years without failure. For the weekend warrior, used with a little common sense, they seem to do just fine. For the guy planning on doing some serious cruising to out of the way places, if you have an older KM2/3P, you might consider looking at the MER conversion using the ZF transmission, price with trans, keyhole adapter and drive plate is more durable and cost less than Yanmar replacement which does not come with a drive plate. If you are planning on using any type of folding or feathering propeller, you might consider cutting your shaft about 1-1/4" shorter and installing a R&D flex coupling sold by PYI to put between your transmission and propeller shaft coupling to reduce shaft loads and dampen engine vibration to the shaft, positive side effect is reduced vibration to the hull, I.e. reduced boat butt.

Concerned about excess movement of the Yanmar engine on the soft mounts, excess maintenance of the packing gland due to high side loads, and wanting some protection from transmission damage from underwater impact from floating debris, a recent strike took off a blade, bent the shaft and distorted the transmission front cover; at our last haul out, we installed a R&D flex coupling and are glad we did, the vibration to the hull has dropped dramatically, the packing gland seems to experience less side loading and our bilge is dry. The flex coupling absorbs considerable thrust loading of the propeller to the transmission, is designed to shear in the event of underwater propeller strike, this should make the transmission happy for years to come.

I had a customer trying to install some expensive soft mounts in his boat last year, complained of extreme vibration from the old Bushings Inc. mounts, admittedly they are stiff. Unfortunately, he had modified the mount, won’t say how, before asking for advice. I explained his boats packing gland was hard mounted to a flange in the hull, no rubber packing gland hose, I explained to his dismay, the engine would move too much on these new mounts, resulting in transmission, shaft or stern tube failure, thankfully he took my advice.

I receive a copy of a photo from a Yanmar dealer, which showed a 3GM30F which had been installed in an aluminum sailboat, with a similar fixed packing gland as mentioned above. The boat yard installed the new engine, not taking into consideration the fixed packing gland; the end result, the transmission output shaft coupling sheared free from the transmission and the hull at the stern tube cracked 8" causing a significant leak. Operating with out a clue, the boat yard called Yanmar demanded a replacement transmission and reparation for hull damage. Looks like the yard will have to eat this one… I have a new idea to market, a cross between a chia-pet and a pet-rock, chia-rock, wonder if these guys will bite.

Long of the short, there are many factors to consider when dealing with engines and the forces surrounding their operation. There are a lot of cool ideas out there to help you get the most out of your boat regarding vibration and impact damage reduction; some that come to mind are the Python drive or AquaDrive CV joint/thrust load bearing arrangement and drive dampeners, these are some of the things that will make your driveline last longer and smooth out the ride.

Best to all,

7

Here’s an update on the MaxProp discussion. WHen I hauled Itchen during a week’s layover in Jacksonville I called PYI, did some measurements and discovered that our MaxProp is 15" instead of the more usual 16". Frederick at PYI said that the 1" diameter difference would have negligble effect on performance or pitch changes. I reset the pitch from 22 degrees to 18 degrees and now get maximum RPM of about 3000 RPM under load, and hull speed at around 2800RPM instead of the prior 2150 RPM. 2400 RPM seems about right for comfortable cruising speed of 5.6 to 5.8 depending on wind & sea conditions. There is plenty of torque in forward and reverse and I think I will leave it there for now, though the numbers indicate that 16 degrees might be even a tad better for optimal 3GM30 operation. What’s interesting to me is that even at the 22 degree setting and consequent low max RPM she handled well enough that I ran her that way for over a year including a run up to Maine and back. Have not refigured the speed vs fuel consumption numbers since the change but I don’t think there has been much of a difference.

Scott