TOPIC: Boat comparisons running 400 Mercury

A few weeks ago, I ran my A/T Sportsman aluminum with the 400 45hp on it. 2 passengers 26 mph. Today I ran the same engine and passengers on my '71 Glastron skiflite 26 mph, all done with gps. The Skiflite is a 100# heaver but no rivits. I thought maybe it would be a bit faster but guess not. Next month I will run my 500 on the Skiflite and see what it does. I am keeping the Sportsman aluminum. New paint and upholstry and a windshild. I would like to see around 30 mph but will take what it gives me.

I get 31.5 mph on my 15 ft cal classic boat. on a good day with no chop. But on a normal day 30 is it. 11 pitch prop.

Since a very small amount of rivets are in actual contact with the water and from what I have read the air bubbles from the rivets may help more than hurt I might look elsewear for the reason. Just like waxing a fiberglass hull will slow it down,the wax fills in the voids and creates more drag.The transom angle in relation to your fixed style adjustment may be a factor. If the Glastron allowed a small fraction more trim up due to it having less of a angle then that can easily make up a mph or two.The sharpness of where the bottom and transom meet also plays into it.Anyway it sounds like your having fun testing and thats what its all about.

Yes this is the first year I have had all my boats up and running. After 7 years working on motors. It is a lot of fun taking 3 or so boats to the lake and trading off with one or the other and making comparisons. I am going to start checking rpm, doing a little trim work and possable prop changes as I go along. I will be running 2 other Merc's and some tiller motors over the summer. Not much water but enough to play.

On my 1970 Glastron SkiFlite I hit 30MPH with a Merc 500 and a 13P prop. (5200 RPM) The lake where I boat has an elevation of 7500 feet. So my Merc 500 is putting out only 35-40HP. Strangely enough, 30MPH was my goal speed too. 12P prop gets me more RPM's, but no faster speed and prop blowout when turning.

I have a 14'-6" all wood construction glen-L zip currently completed with a 100% Restored Mark 58. 45hp with an 11P 2 blade prop I get 31 MPH.

Travis

So I'm thinking, my 500 with the right prop and at 4,000, 30 mph is not out of the realm of possibility. First, I have to check the rpm's and the total advance. I have only ran wot for a couple min. Then I could play with the trim angle until I getting the best I can. If I can get the A/T aluminum up around there, I would be happy with that.

to get 30 mph you will be at about 5200-5500 rpm 4000 gets me about 24mph depending on trim.

Woops, I was meaning 4,000 ft elevation.

1030hugo,
What pitch prop are you running?
doc

I don't know, I will look and see if it is stamped on it.

Having a real problem reading the numbers. It is a Quick Sliver prop.
I see a 10, and it measures out to be a 10" prop. some numbers proceding the 10 are (4 ###5A2 10) also has D8J stamped on it nearby.I have tried steel wool, black marker, but that is all I can get.
My 500 has a brass prop 48-22105A2 10 So that may be the same number. They look the same when checking the pitch and diameter.
I know I have the horse ahead of the cart here. Need a tacometer to check rpm and then also verify the timing. I know the timing is close, but don't feel comfortable running wot for more than a minute.

Dealerships typically have a box of used tachometers they have removed when installing a new motor and related gauges that they will sell cheaper than new ones. $30-$50 compared to $100 +/-.
Ask for one that reads off the stator (or alternator) and has a '4p' setting on the back.
Set the tachometer to the '4p' setting, attach the 'send' wire to the kill terminal on your magneto - leaving the original 'kill' wire on the Merc attached, the ground wire on the tachometer to either a good powerhead ground or the 12vdc boat battery (-) if you have electric start on your Merc. You can also attach the '+' terminal to the (+) on the battery through an off-on switch if you want the tachometer light to function.
Wired this way, the modern tachometer designed to read off the motor's alternator (stator) can be successfully used on the old school magneto to monitor your RPMs.
note:
There is also a '4c' position on these tachometers, so make sure you use the '4p' rather than the '4c' position.
Doc

Thanks Doc, I have a couple of tack's in some of my box's of stuff. I will dig them out and see if one will work.
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