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I did not intend to ignite more rage over the Sherwood vs. Oberdorfer debate.

Someday I may opt to buy the Oberdorfer pump, but I still wince when I see how much smaller its pumping cavity is. Two years ago I posted some calculations to back up my concerns over its lower capacity for motors over 30 hp. But I realize that many people use it on their 35 hp M35B motors and are happy with it. I am not ready to try it now, but maybe someday.

The simple fact is that a third company has now come out with an all-bronze knockoff of the Sherwood at a fraction of the cost (around $400). That's worth discussing. Competition between different pump companies is good for the consumer.

I am not bothered by "backwards" direction of the Sherwood pump cavity. I'm able to get my skinny fingers behind it to remove the 3 screws, and to pull the cavity off the impeller without having to disconnect the hoses. However I am bothered by the potential for rust causing failure of the G908 bearings. So the opportunity to buy an all-bronze Sherwood knockoff for $400 is worth my consideration. But only if I can confirm that JMP is a reputable pump manufacturer, and that it matches the pumping volume of the Sherwood. That's the reason for my question about cross-compatibility of the impellers - that would answer my question about its capacity. I know that JMP recommends using their impeller - every company recommends using their own replacement parts. But if JMP is selling their replacement impeller for use in the Sherwood G908, that suggests that the pump cavity is the same size.

So rather than beating the Sherwood vs. Oberdorfer horse to death, I'd love to hear comments from someone who has actually seen the JMP version.

EDIT: I just answered one of my questions. JMP sells their own replacement impeller (#7172-01) as a replacement for the Sherwood impeller (Westerbeke #200175). https://www.jmpusamarine.com/products/7172-01k-jmp-marine-flexible-impeller-kit/

Therefore, the pump cavities are the same size. Based on this, I might purchase the JMP and keep my Sherwood as a spare. I'll think it over some more, and look to see if there are happy customers out there somewhere.

Did you end up purchasing this? I'm looking for recommendations, since it is all bronze and priced much more reasonably than Sherwood's new bronze pump.

Is the pump cavity the same size as G908, or is it smaller like the Oberdorfer? Will it use the same replacement impellers as the Sherwood version?

Kinda begs the question -- Why the heck don't they just pre-stretch their belts? 
Remember pre-shrunk clothing?

Perhaps you can ask them.

However, in my experience (which is admittedly more limited than yours) there is much more than stretching happening. Specifically, as the belt wears its cross-section changes. My old belts are considerably narrower than new ones that replace them. The v-shape of the pulleys causes this, and the belts are pulled further into the pulleys. This happens gradually over the lifetime of the belt, until they sink so far into the pulley that the alternator is close to the end of the bracket. Then it's time for a new belt. I measured my last belt and it had lost about 1/16" of width at the top (i.e., went from 3/8" wide to 5/16"). Holding the new belt next to the old one made it really obvious. I threw out my old belt, but next time I do a replacement I'll snap a picture and take some caliper measurements.

I previously thought that the rubber was abrading off the sides of the belt. But since there is little or no no black powder in my engine cabinet, it's possible that the cross-sectional shape might actually be changing (getting skinnier but also taller).

I'm sure there is stretch happening also, but the belt sinking further into the pulleys as it gets narrower is definitely a significant factor. Next time (in a few years) I'll take some more pictures and do some more measurements.

Breakin : To loosen the belt the last thing that I'd ever do is to screw with the nuts on the water pump pully!?! 

I just loosen the adjustment on the alternator and pivot it!!

OK, so let's tension that new belt at 130 lb. In order to move the alternator I'll need 225 lb of force. [=2*130*cos(30°)]  I'll continue to take the extra minute it takes to first loosen the screws (not nuts) to release the tension.

How are you measuring the pressure?

I move the alternator out 1/8"-1/4" at a time, then use the Krikit gauge after re-tensioning the belt. I use an ultra Sharpie to put marks on the alternator bracket to keep track of how far I've moved it.

a new belt loses its tension pretty quickly as it runs in.

Next time I have a new belt, I'd start at around 90 lb and watch to see if it drops to 60-70.

Covered here for 3/8" a belt:
https://c34.org/bbs/index.php/topic,11728.msg94969.html#msg94969

Install a NEW belt at 130 lbs. then run it in and re-tension

I installed my new belt in April. I saw your linked post yesterday. I also saw where you said, "Besides the max tension isn't what to use -- use the minimum tension that does the job," which is why I'll try 90 next time and hope it settles in around 60. If not I'll go higher.

Another trick: Take a 1x3 or 1x4 piece of wood (about a foot long) or similar. When you loosen the bolt on the alternator, the easiest way to move it is to put the end of the wood against it and gently tap with a hammer. then re-tighten the bolt before re-tensioning the belt.

I'm finding that a new belt loses its tension pretty quickly as it runs in. I've gone from 60-70 lb down to 40 lb a couple of times with my new belt. I'm still re-adjusting it to get it to stay at 60-70. Next time I have a new belt, I'd start at around 90 lb and watch to see if it drops to 60-70.

Here's my easy way of de-tensioning and re-tensioning the alternator belt for adjusting the alternator position (i.e., increasing the belt tension). It works great for my M35B with original 50 amp alternator. Not sure about other motors or other alternators:

Loosen bolts attaching pulley to coolant pump. Remove the one furthest away from the belt, if needed. The pulley pivots, fully de-tensioning the belt. Then you can loosen the alternator bolt and easily nudge it out 1/4"-1/2", and re-tighten everything to re-tension it. If the resulting tension is too much or too little, repeat and re-adjust. It's really quick and requires no special tools:

If you have not done so already, I suggest that you purchase a battery powered carbon monoxide alarm right away and install it in your aft berth. Black soot on the interior is a big red flag suggesting that you have toxic exhaust gasses also entering the interior. If you go down below with the engine running, you may get CO poisoning and you will not know what hit you. It's a hidden killer.

This is what Shamrock has, I really like it.  I disconnect the chain and use the drum with spare halyard to ascend the mast, pile up 10 feet of rode into the anchor locker and use the drum and halyard to lift dinghy to deck and many other uses.  It's a Maxwell freedom series, believe chain wheel, drum or both were options.  You may be able to contact Maxwell and have your existing windless modified. 
Jim

The anchor locker lid has a hole in it when the lid is closed the drum is above the lid.

Jim,

Your anchor locker design is totally different from mine. Pretty surprising for a boat that's the same model year, and only 35 hulls later. Are you the original owner? If so, did you request a special upgrade for your windlass, or did Catalina make a running design change?

My locker hinges are on the port side, latch on starboard, and my water tank opening is to port, but under the hatch. My Maxwell 500 windlass with capstan is horizontally mounted on the starboard side with a single foot switch (up only). I'll try to get a picture of it, but right now I'm 800 miles away.

I'm curious what configuration pbyrne has on his boat. If it's the same Maxwell 500 as mine, it (and the chain gypsy upgrade option) have long since been discontinued. I've read about many people searching for the gypsy upgrade unsuccessfully. (I probably read it here, but maybe on another forum.) Never hurts to try to find one, though.

I looked at the Gates calculator. I think that calculator gives the recommended tension that the belt can withstand. How much side-load the water pump and alternator can withstand is a separate (unanswered) question. It could be higher, it could be lower.

Hmmm... Maybe I should have purchased the Krikit that goes from 50-150lbs then?

That's the one I have

I selected the 100-300lbs version based on the Marine How To article here: https://marinehowto.com/marine-alternator-installation-tips-tricks/ which is also the article that suggested using the Gates V-Belt Tension calculator.

That sounds very tight to me too, but one thing I've learned is that if Rod says to do something, it's a good idea to do it. I'll have to read over that article and see what he said. Every time I think I've read all of Rod's advice, someone comes up with something else that I missed.

I guess one important question is what is the designed side-load limit (beyond which bearing failure is accelerated) for the water pump and alternator? If I knew those limits, I'd divide the lowest one by two (since side load = 2x tension*cos(belt angle)) and use that as the maximum allowable tension.

["the sea water pump....require daily inspection"]

Could an issue with the raw water pump have anything to do with causing the alternator failure? I can't imagine it could, but maybe there's something I'm missing.

Seems that the bulletin was updated at one point to indicate that Westerbeke had determined poor maintenance was the cause of the issues, not the missing collar.

In a word. No."

In Westerbeke's typical fashion, SB 235 was updated to point the finger toward the owner instead of to the faulty designed IRON pump that can seize up. 
"the sea water pump....require daily inspection" Really? REALLY?  The pump is so badly designed that it needs to be inspected EVERY DAY?

The ring on the camshaft was simply a bandaid (a very slight hedge against a seized pump.)  As you may know, Westerbekle has finally wised up and retired that G908 pump and replaced it with a proper "marine" BRONZE pump.

Just curious, the G908 has a bronze pump cavity. Only the part that mounts to the motor is cast iron, and Depco painted mine when they rebuilt it, and I have not seen any rust. How does changing that part to bronze reduce the likelihood of bearing failure? Have the bearing materials been improved in some way? Are you recommending the new version of the Sherwood pump as a worthwhile purchase?

Once you get that sorted...be aware that due to our tanks NOT being square, the gauge is only "correct" when it reads 100% full and 100% empty.😎

Actually mine is not even correct at those points either...

Thanks for all the info and suggestions everyone. I was able to find essentially the same alternator as what I'd taken off, at a local shop. Based on the discussion here, I decided that was the logical way to go for now, with an upgrade to a larger, externally regulated alt in the near future. This one will become the backup. Interestingly, this new Mando claims 55 amps, while the old one claimed 50 amps...

Could you post the model number? It might be handy to know if my alternator should fail in the future. Drop-in replacements are always good to know about.