reviving old seacraft (propeller question)

[NoBones]

Hi, and thanks for this cool website!
I recently got a '69 seacraft center console with an 80's carbed Merc 200 V6. I know it's way too much engine for this boat,

Whats you talkin' bout Willis !!

200 ponnies is perfect on the 20SF.

When you need to GO It is nice to have......
21 inch Laser II on the NoBones

PS: Welcome to the site bitsamonkey..

See ya, Ken

[eggsuckindog]

I second that on the 21", I have a T Top and a Master Angler and run a 19 at 5600 so you need a tad more.

[bitsamonkey]

Thanks for your help on the prop. Now to the next issue...
The boat has a HUGE tank that takes up the entire console, including the forward seat portion of it. Have you ever seen a seacraft with an external tank like this? Or do you think someone abandoned a bad tank under the deck? It is a '69 and I believe that's the first year for these. It does not have any storage cutouts along the under gunnel liner like all the boats I've seen in your pictures. In any case I'd like to have an under deck tank and a smaller console.

[Bigshrimpin]

The older boats had above deck 40 gallon fuel tanks.

[Blue197320]

no bones and egg what diamater prop are u running? no bones i know ur boat is fast with that merc u have. egg what speed do u get out of yours?

[eggsuckindog]

My prop is standard issue Merc SS and not sure dia, my motor is mounted high and I cannot get any trim before it blows out. I will put a Mirage Plus on it for more rake in the blade but my top is a miserable 48/50 with it dragging so much hull, it rides too flat for any top end.

[Fr. Frank]

Dixon, have you measured the angle of thrust on your motor at operating trim angle? If you cannot trim at all without ventilating your prop, that means you're probably at a negative trim angle (thrust angle aims slightly downward), and if so, you're running too high out of the water. You need a positive thrust angle of at least 4-5 degrees, or you're literally driving the bow down into the water, creating a lot more drag. You want to get the stern up, then you want to lift the bow for best speed. If you run with your motor trimmed all the way down, put a carpenter's protractor on it and measure the angle to the cavitation plate. If you don't have access to a big protractor, just stick a long level or good straightedge along the keel line of the boat. If the cavitation plate is exactly parallel with the keel line, or the front of the cavitation plate is higher than the rear, you need to adjust your mounting height upward. You need about 10* of negative trim (trim "in") to get on plane, then you should run at about 4*-10* of positive trim (trim "out" or "up") at full throttle.

[CaptLloyd]

If the cavitation plate is exactly parallel with the keel line, or the front of the cavitation plate is higher than the rear, you need to adjust your mounting height upward.

Fr. Frank,

Could you verify that for this situation, the motor needs to be mounted higher?

Thanks,

Lloyd

[Fr. Frank]

If the cavitation plate is exactly parallel with the keel line, or the front of the cavitation plate is higher than the rear, you need to adjust your mounting height upward.

Fr. Frank,
Could you verify that for this situation, the motor needs to be mounted higher?

OOPS!! I make a boo-boo. Sorry, guys.

Assuming a transom mounted engine, if the situation is just as described, where the motor ventilates too easily when trimmed, then no, the motor needs to be mounted LOWER.

LOWER LOWER LOWER

This should increase performance AND efficiency. It's about the angle of attack. The idea is to be able to fine-tune the angle of attack without introducing air to the back edges of the propeller blades. How much lower to mount is the unknown. I'd go one bolt hole to start.

[sergiman]

hi ken, i was wongering what year your boat is and if it came with the rail, mine is a 1978 20' and came with no rail,and i would like to put one on it, great looking boat by the way, thanks mike.