[m&mmariah]

We plan on taking our 1996 shabah 180 to Lake Tahoe this summer (6225 feet elevation). The Shabah has a 4.3 mercruiser with the 4V weber carb. The boat will be loaded with me, my wife and our small dog. We just plan on cruising around, about 3000 rpm, no towing, just sightseeing. I currently have a mercruiser black max 21 pitch, and alpha 4 20 pitch, and a black max 19 pitch (all standard mercruiser aluminum props).

I think the 19 pitch prop might be ok, but I suspect I might need to buy a 17 pitch, due to the reduced power at that altitude. I just hate to spend the money for two day's worth of cruising on the lake. Any advice?
Thanks!

[mikeyt]

I'm not gonna pretend to be an expert on props at higher altitudes but here's what i know. Power loss is about 4-5% per 1000ft increase in altitude. The decreased air density means your boat will run rich (with the carb) so you will burn a lot more fuel and lose probably 25% of your power. I'm guessing that you could therefore see a 10-15mph drop in top speed. You could change the carb jets or adjust the carb to make it run leaner while at Tahoe (be sure to change back once you leave) and make use of your 19" prop and that should reduce your loss of performance. I suspect though that it will take some 'fiddlin' to get the boat performing like it does at sea level and given that you are only there for a couple of days it may not be worth playing with the carb unless you plan on returning on a semi-regular basis.

Also, i wonder if there is a 'rent-a-prop' program at Tahoe? Knowing that many boaters come from lower altitudes & require a prop change, it might be worth looking into?

[ColoradoDiablo]

I am running a 17p Solas 4 blade at 7000ft ( I live at 7200 ft) on my 18' 4.3 Diablo. It runs right in the 4300rpm range. When I did run a 3 blade 19p it ran at about 4000rpm WOT.
Do you have Smart Tabs? If so the 19p will work fine. It will work for the couple of days your there anyway. Just gonna take longer to get er up on plane , and your gonna have to run faster to stay on plane.
Mikey hit it right on the money!
I'd save my money , cruise it with the 19p prop , turn the air screws out a 1/2 turn , and buy more beer for camp! LOL
Larry

[m&mmariah]

Ok, thanks for the advice! I think like you said, the 19 pitch will be fine for a couple of days, and I'll have to adjust the idle speed stop screw a little be to make up for the thinner air--don't really want to mess with the idle mixture screws, as it would involve hooking up a vacuum gauge while on the lake. I think I read someplace that the correct idle speed for the 4.3 is 750 rpm with the drive IN GEAR. Correct? Again, thanks for the help.

[ColoradoDiablo]

650-700rpm on my 92 LX. Anything over 1000rpm and you'll eat the clutch dogs. 750rpm ought to suit you fine.
BTW , have fun and take some pics!

Larry

[Dredd]

Seems like it'd take quite a few trips to make up the savings in gas. Interesting topic though.

Sounds like a fun trip. Take lots of pics!

[m&mmariah]

Ok, will take pics & figure out how to post them! I'm envious of everybody who has a fuel injected motor.....no need to mess with idle screws, etc.......You lucky basta......uh, you lucky dogs!

[shanestiehl]

Might I suggest a quick build of a Hydrogen Dry Cell ..It will help give you way better fuel millage then you have ever had. I'm not a sales man I'm a user and it does work. but I have the sam eboat as you and was curious if you answer a question. You see I just bought my 180 shabah 18' with a 3.0 mercrusier and Alpha One but It says to turn fan on but I dont hear or see any fans back there . The exhaust duct that mounts under the back top deck is just laying down by the builge. If it had a blower where would it be located and does your bout have a drive gear oil reservor? If so does it use much Drive Gear Oil? But seriously a Hydrogen cell is the way to go..also you dont have to worry about atmospheric Changes when burning hydrogen. ..Look it up on You Tube.

[m&mmariah]

Shanestiehl, the fan/blower is turned on and off by a switch on the dash. The fan is essential to ensure that there is no gasoline vapor in the engine compartment. Gasoline vapor is heavier than air, so any vapor will be at the bottom of the engine compartment. The tube you see in the engine compartment sucks up any vapor from the bottom of the engine compartment (because that's where the heavier gasoline vapor will be), then exhausts it out one of the vents located near the swim deck. You should leave the fan running at least 5 minutes prior to starting the engine, as well as when idling along under way, to ensure there is no build up of fumes. We don't want to torch our boats!!

Hydongen generators are a bit esoteric for me, but I look them up on google! How about posting some pictures of your Mariah?

[ColoradoDiablo]

[QUOTE=shanestiehl;35398]Might I suggest a quick build of a Hydrogen Dry Cell ..It will help give you way better fuel millage then you have ever had.

Really ought to start a new thread , but....

I can't see one of these things standing up to the extremes of the marine enviorment , fuel mileage increase maybe...what does it do to performance? Got any hard facts that this is a viable addon? Or just another gizmo like the water injection kits of the 70's.
JMO

Larry