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Hey guys I am restoring an old hydroplane. I was wondering if I can get some feedback on the proper height of the motor. if I measure from the bottom of the back of the boat, keep in mind this boat has a completely flat bottom. how much of the lower unit should be under the bottom of the boat? the motor is a yamato 80.
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An 80, the 20SSH minimum height I believe is 1/2" below the true bottom As an older hydro it's a guess, if you can post a pic or post the kind of hydro it is someone might know specifically what to add. Good LuckTeam Tower -
I'm guessing that you are not intending to race this restored boat. If that is the case then there is no need to worry about what the max legal height is for racing. You would probably have more fun with the boat if it planed off quickly and had no issues with cooling the Yamato. In this case a couple of inches below the bottom wouldn't be too much.Comment
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Hydromann wasn't clear as to what part of the lower unit he was describing.Originally posted by pops67g View Post
Pops67g do you mean a couple inches from the bottom to the center of the prop shaft?
The Y80 measures about 16.4" vertical from the rear corner of the transom clamp bracket to the prop centerline. At a couple inches that would make the transom about 14-1/2" vertical up from the bottom to the rear top corner of the motor board, not measuring along the slope of the transom.
Hydromann post some pics, sent you a PM
"Keep Move'n" life is catching up!
No man's life, liberty or property are safe while the legislature is in session.Comment
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With my DSH, the usual short course setup has the prop shaft center at about 1.5 inches below the bottom. The water on a short course stays lumpier than on the longer ones so it helps get a lot more bite and acceleration. 2 inches below the bottom for playing would not be excessive in my opinion.Comment
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I agree that if not racing going lower has advantages, you want to be high enough for it to air the prop & hull some but take off from a start & running acce
leration are also important & fun. To be sure the boat is in the ballpark for an 80, how long is it & what's its weight ?Team TowerComment
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That's good, no problem for the 80. As a fun boat I find that to run a boat 1 class level up from the motor is good in a way because you might have to deal with wakes or stuff not often found on a closed race course. Definitely old style, it might be a D or maybe a C. A lower pitch prop is what you'll probably find works best.Team TowerComment
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Would that be the brass prop that was original from Japan. ? Is the shear pin at the rear of the prop close to the gear case cone? If so the prop shaft is the original metric unit used in Japan racing. They ran the engines deep compared to what is done in the US with these engines. Here is the Y80 manual
http://yamatoracing.com/y80manual.pdf
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Thanks for the info this boat came with the 80 on it but it could have never run the way it's set up? The prop shaft was 2 inches above the bottom of the boat? First hydro project.Comment
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Odd transom height, but who knows what it was for at the time. I'd think setting it up for as much as 1-1/2 deep & go from there. That's low enough to run & not too low to shim up a bit if you wanted later on. 1 question to answer: is the prop you have [origonal Yamato?] a surface prop?
Team TowerComment
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Set idle screw for best idle in water, go rich till stumble then lean till about to die, then to the middle of that. The high speed is sensitive and engine dependent on: fuel, fuel oil mix, plugs, mag advance, temp, humidity, etc. Mine is set at about 7/8 of a turn open from full closed. Can only get just right by testing with speedo and tach and reading the plugs and piston crown. Too lean bad for the engine too rich puke power. I am using NGK B10EGV (part # 5927) plugs with 18mm to 14 mm adapters. These plugs work better than the 18mm NGK A9N stock plugs that it came with and are easier to read.
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Sorry guys one more question is it possible to set up a tachometer on the Yamato?Comment
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You can use a MyChron 4 system (monitors RPM and cylinder temp) or other simiilar device. They run around $350 or so, can find on kart sites or eBay. TinyTachs are a cheaper alternative but hit or miss on reliability (I never got them to work effectively on a 102 or 302 - love the MyChron 4 though). -
I have a Y80 and cannot get a reliable reading on the Tinytach (old model TT226R-1C), apparently a dirty signal from the points mag. Someone suggested to wrap one of the plug wires with alum foil to prevent the tach from picking up stray signals, I will try that. My TT works great on my Merc with CD ignition.
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Hydromann, where are you located? Chances are that a stock outboard racer is located within driving distances, and I would highly recommend that before you go out on the water, someone else takes a look at your setup for 2 reasons. Obviously performance but more importantly safety. Insuring that your steering setup is good, tuck of the engine, not just depth, and several other factors will give you a pleasant experience and not an ohhhhh carp (or substitute another expletive!)When it comes to boat racing and the wife, it's easier to ask for forgiveness than it is permission, and of course I spent a number of nights sleeping on the couch!Comment
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thanks for that info, I am located in the pompano beach area. first test run went well, definitely need to cut down the transom another inch. boat ran good but the motor needs to be trimmed up and bit, too much cavitation if I trim it up. for a fun boat I don't need to be walking that fine line you do when racing
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