TOPIC: A weighty issue

Took the 18' Nordic out again briefly, 1975 Merc 1500, 15 pitch 3 bladed prop, mile-high altitude, you have the picture.

It was frustrating; the motor would try to accelerate, but would not get up on plane and would eventually lug out and die.

I got out, to go get the trailer and set up on the ramp, and they motored off. I came back, got the trailer in the water, and....where are they?

As soon as I got out, the boat took off and was working great. Up to full speed, cutting and turning and sliding sideways on tight turns. (My 16 year old is finally driving).

3 people ~500 pounds, okay. Add myself and we are close to ~800 pounds.

So... Looks like I need to find a prop with less pitch so I can get more pulling power. Can y'all suggest some compatible ones? Alluminum preferred to save some money. Speed is not an issue as much as accelleration and pulling power. (I wanna go ski someday!)

Something is wrong here.

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Either the boat itself is too heavy ( water logged )or the motor is not making proper power !!

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So for step one I would make an appointment at a shop that has a " Marine Dynomometer "

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they will tell you, yes your motor is fine or that it needs work.

Well, I suspect its just a heavy boat. 2 large fuel tanks, no leaks though when I take it out there was no water when I pulled the drain plug.

It was frustrating; the motor would try to accelerate, but would not get up on plane and would eventually lug out and die.

That is a scary sentence to read. Sounds like your on the fast track to melting a piston.

I guess check everything over. But if its still lugging, dont do that. These 1500's dont like to be lugged. That is the death of them.

When you feel RPM drop when its struggling at full throttle , that is NOT GOOD.

Conrad

So what prop should I use to get more pulling power and get the motor back up into a proper rpm- powerband?

So what prop should I use to get more pulling power and get the motor back up into a proper rpm- powerband?

Well what RPM was your 15 pitch producing at WOT? If its in the low 5000's you could stand to go down to a 13 pitch I guess.

You want that motor to turn 5800-6000 RPM at full speed. Lugging it down at 4800-5200 is not good at full speed.

Of course there still could be something else wrong with your motor too. I have no idea what boat/weights we are talking about.

Conrad

I got a good answer on antiqueoutboards:
Your boat weighs 1500 pounds according to this link:
www.nadaguides.com/Boats/1986/Nordic-Boats/SCANDIA-18OUTBD-Fiberglass-7-0-0/Standard-Equipment/Print

Apparently the inboard version of this boat features 360-454 Cu In V8 engines for skiboat use.
So, that may indeed be my answer. I need more power, scotty!


with less weight on the boat I was getting 5900 rpm and 39mph at WOT.
With all the weight in the boat, it was lugging, like 3000rpm and 12 mph.
So yeah, less weight, less pitch, sell the motor and but a 300hp.

I still suspect the motor. 1500 pounds seems optimistic, since Nordics are hand built. Even if true, 150hp should push it about 50. I used to own a Bayliner 1800 Cobra, 1400lbs, 125 Force, ran 45mph at 5500rpm's. Unless that Nordic has 500 pounds of ballast hidden somewhere, suspect the motor. My two cents worth.

From my computer I can only offer educated guesses, but your outboard does sound to be the problem.
However, many older boat hulls gain a great deal of weight due to water logged foam flotation. You might consider taking your boat outfit across some truck scales (some truck stops have these).
If the carburetors still have their "Back Drag" jets, these jets will yield these symptoms. Although a picture is needed for a proper explanation, these can be removed rather quickly (one per carburetor - please remove all three jets) to test for this problem.
"Acceleration Holes" are also a tremendous help when added to even an aluminum propeller exactly for the problem you are having. These are seen standard on some performance stainless steel propellers.

Joe
www.fergusonpoolemarine.com
This email address is being protected from spambots. You need JavaScript enabled to view it.

It is either the boat or the motor !!!

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A simple test run at a shop that is equipped with a " marine dynamometer " is a must here.

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Trouble shoot and leave the " guess work to others "

That will be something I try next, after I test out a new prop. I picked up a 13 pitch 4 bladed prop yesterday, to replace my 15 pitch 3 blade. We'll see how that works.

A marine diagnois will be cheaper than if you melt a piston as on suggested earlier.

Using a prop with less pitch will allow even a motor in poor condition to rev at 5500 RPM again.

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That still does not confirm that everything is OK with the motor.

I am trying to find a place with a dyno.
I'm also looking to find out what a rebuild is going to cost me.

Excellent,---you are now taking positive steps to prevent possible major expenses.

Just remember if you dyno that 1500 at the propshaft it will not produce 150 hp.

More like 115-125hp

Conrad

I'm thinking part of the problem could be related to one of your first statements,..."mile-high altitude,".
Unless someone has already re-jetted for that altitude the poor beast is really struggling.
If that has been done already and she still is struggling as described - I'm with the others in that you had better stop running the beast until someone can load it via a Dynometer and see if the problem can be identified before she dies a sad death.
Thom