Probably a simple question
 

Excuse me if there is a simple answer to this :party-smiley-004: but how come boats don't or at least very rarely us multiple speed transmissions, like say a TH-350 or powerglide?
Wouldn't this allow the prop to spin faster?

Simply put "cost" and available "room"! Merc played around with a trans a few years back called the Blacktrac and it worked well but was mostly used in cruisers. Racing ski boats use TH400's in them to maintain a decent rpm at 100 plus skiing speed.

Would ear muffs on drive be enough to flush at home ,or would I risk overheating?

If you have a Bravo drive be sure to get the Bravo flushing muff it has a SS wire that passes through the water inlets so the muff cant fall off. If you have a cheapy on then make sure to have someone watch it incase it dose fall off. Low water pickup drives take a speical flushing adaptor for them. Your garden hose will supply more than enough water to run your boat. Don't believe that crap about blowing out seals turn your hose on full bore the motor will take what it needs and keep your rpm's under 1500.

Funny you should mention that - I fought with a water supply issue for a couple of hours last night, trying to fire up a new 489 in my boat - standard Bravo pickups. I was using the Quicksilver muff that has the wire as you mentioned, and was getting no water flow. I took the hose off the transom assembly and put the garden hose in there, and was getting plenty of water out the exhaust. Figured I had an air leak in the drive or transom assembly causing the pump to lose suction, or possibly a weak pump. I tried 2 different sets of the Quicksilver muffs (one with the hole opened up for better flow) to no avail, and in a last ditch effort at low hanging fruit before tearing into it, I put on a set of the el cheapo WalMart wire spring muffs. Voila! Water out the exhaust! As you mentioned, I had to get down there and hold the muffs in position over the drive intakes until the pump built enough suction to keep them there. I still don't know what the deal was with the QS muffs.

Hmmm, we got sidetracked a little bit from talking about transmissions in boats, didn't we? ;)

I thought the issue was also the fact that the load is never removed from the driveline to allow it to shift, i.e., it never coasts like it does in a car. I guess a torque converter may be able to get around that, but then you have the additional cooling issue, room, and weight. Someone had experimented with a special prop that would change pitch at a certain RPM. Don't think it would hold up to high power applications, however.

The only thing it would help would be for docking the boat and planing off. It would not help your top end, and it would only help with docking if you had a really big prop. Some boats do run 2 speed transmisions with the speedmaster drives.

A constant velocity transmission like used on sleds & quads would be interesting. I’ve seen them used on 350hp turbo RAVs (quad) with success. Obviously it would have to be beefed up to support the power some of these boats are putting out but weight & space would be minimum. Just a thought.

Mercs water pump is a really good unit but the problem we see is the "suction" hose inside the boat. The factory uses a semi-rigid hose with a wire inside of it to prevent suction colapse. Sometimes this hose has a low dip in it (lower than the pump) and this can cause an air-lock on flushetts. That could be what happened to you??

Everyday,we must deal with what was referred to the ecology ,if we give sufficient attention,then we can see that many things we have in this matter