reviving old seacraft (propeller question)
 

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, but it's what I got.
It gets this little boat going in a hurry, but seems under propped at wot. So I was wondering what size prop you guys that have similar rigs use. The boat is super light with no top, no livewell, no extra nothing and will stay this way.

Re: reviving old seacraft (propeller question)
 

19 pitch Mercury Mirage Plus . . . if you carry a heavier load 17 Pitch Mirage Plus will work well too.

Re: reviving old seacraft (propeller question)
 

Whats you talkin' bout Willis !! :eek:

200 ponnies is perfect on the 20SF. :D

When you need to GO It is nice to have......
21 inch Laser II on the NoBones http://i7.photobucket.com/albums/y27...Picture117.jpg

PS: Welcome to the site bitsamonkey..

See ya, Ken

Re: reviving old seacraft (propeller question)
 

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.

Re: reviving old seacraft (propeller question)
 

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.

Re: reviving old seacraft (propeller question)
 

The older boats had above deck 40 gallon fuel tanks.

Re: reviving old seacraft (propeller question)
 

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?

Re: reviving old seacraft (propeller question)
 

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.

Re: reviving old seacraft (propeller question)
 

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.

Re: reviving old seacraft (propeller question)
 

Fr. Frank,

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

Thanks,

Lloyd

Re: reviving old seacraft (propeller question)
 

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.

Re: reviving old seacraft (propeller question)
 

Hi Mike, The NoBones is titled as a 1970 built 11/69.
I bought the boat in 1989 from the original owner.
It was beat to death when I got her.
In 1980 the owner sent her back to SeaCraft to get re-done.
The Teak spray rails were added at that time.
We have discussed these rails here before. With the sharp entry of our hulls the rails help to deaden the re-entry and throw the spray away from the boat. I have been in 20's & 23's with and without, I'll take with....

See ya, Ken

PS: Thanks for the compliment.
BTW: As you are in Brunswick you should really try
to join us in April at Long Point. Check the gathering section for details.....

Re: reviving old seacraft (propeller question)
 

Hey Bits,
BTW I like the moniker.

I have an`89 20 sf w/ a `96 Ocean pro 150 w/ good comp and finally runnin right after carb rebuild and etc, etc. I have a mich 14 1/2 X 17 wheel . Not sure if it`s an apollo or rapture, but from the bow lift I get, I would guess it`s a rapture.
I recently scored a 15 3/8 X 17 mirage plus at discount marine stuff in Stuart for a sly price. I will do a definitive ramp test when I get a new tank in.

I hate going to work, it interferes w/ my passion.

Fr. Frank and BigShrimpin were kind enough to enlighten me as to the subtleties and needs for our friends. Bow lift is BAD. Stern lift is necessary. This really hit home when I was home in Ma. on my brother`s Hialeah Mako `22. It has tabs and I don`t, but the angle of attack was very tight and it didn`t pound in tight chop as I experience. Maybe that`s why my console screws were floating? :eek:

I now spin 53/ 5400 at 37-39 mph gps 2 way run w/ 3, less than human, life forms, bimini and 210 lbs fuel last time coming in.
My brother Paul thinks I`ll only gain 2-3 mph , but I`m hoping for lotzzz more in many different ways. 45 anyone? Ok, maybe I`m a little optimistic. Ok , maybe a lot.

I`ll be happy with better overall handling and a nice big bite in a following sea.

GFS

GFS

Re: reviving old seacraft (propeller question)
 

ken, sorry about that, no i meant the hand ss rails on the top of the hull. i have the teak rails like you said, and yes i will be coming down to longpoint,should be a great time time, can't wait to see the boats, a meet everybody.mike

Re: reviving old seacraft (propeller question)
 

Mike, glad you are coming to Long Point. By the looks of it
we all may need to stay till Monday just to
sober-up :rolleyes:
I custom bent the grab rail on my 20 during the re-do.
Bought the stock from Surplus Unlimited in Daytona...
See ya soon, Ken

Re: reviving old seacraft (propeller question)
 

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.

Re: reviving old seacraft (propeller question)
 

Frank- Its all the way down on the transom now but its not that bad, I just can't get much more than a few degree's positive, just need a prop with a longer blade/rake and cup. Very similar to my 23 when we put the V8 on, the SST wheel would cavatate on the flats but a big long blade Protester was the ticket and you couldn't blow it out if you tried - which I did :D I think a Mirage + or Tempest will do fine, need a 19

Re: reviving old seacraft (propeller question)
 

I agree on the Mirage+, it's a great prop. But you may need a 17 or 18 to get max RPMS while heavily loaded. What kind of prop are you running now?

Re: reviving old seacraft (propeller question)
 

Standard Merc SS wheel with round sort of Mickey Mouse ear looking blades, probably great for most applications, gets the boat up very smooth and good at cruise.

Re: reviving old seacraft (propeller question)
 

I understand you're running a Black Max prop. What diameter and pitch? Have you ever had the cup increased? What are your max rpms now, fully loaded at max gross weight?

Re: reviving old seacraft (propeller question)
 

Not sure on Dia but its a 19 and no I haven't added any cup, to do that would bea 1/3 of a new one. 5600 rpm

Re: reviving old seacraft (propeller question)
 

Dixon, a couple more questions:

Do you have a negative trim limiter, such as a rod extending from one side of the transom mount to the other, which limits how far down the engine will trim?

With the motor at neutral trim (cavitation plate exactly parallel to keel line), how high above the keel is the bottom of the cavitation plate?

I'm trying to figure out if you're cavitating or ventilating, or both. The fix is different depending on the cause of the air on the blades, because the cause affects where/how the air enters onto the blade, and produces the most vacuum.

If you're cavitating (or mostly cavitating), the fix is to change the angle of attack and departure angles on the blades by greater progressive rake, and/or increasing diameter of the prop, and/or increasing cupping, and/or increasing blade tip size.

If you're ventilating (or mostly ventilating), the fix is to increase the ability of the thrust side of the prop to hold water while surfacing, which is accomplished with increased cupping, and/or smaller blade tips with lots of cupping and reduced blade flex.

I'd like to actually see your boat out of the water in person, and have several props to try at once. I can bring my 15.25" x 16.5" PowerTech. You probably have the 14.5x19 SS Black Max, which is a mid-range propeller.

I can get a couple of different props to try from AAA Outboard, in different style and pitch. Just gotta set up a date and meeting point that works for both of us, if you're interested. And no, you don't have to buy any props. It's just nice to know what works best.

Maybe I can bring them to Long Point, unless you want to do this earlier?

Re: reviving old seacraft (propeller question)
 

It will trim negative a bit I think, I only get cavatation when I try to trim the bow for maximum top end. The prop just doesn't pull the bow up much then looses grip, its not bad except for attaining top end which I know could improve. I will probably be able to find a couple Mirage's at Longpoint to try maybe, as they a readily available on the used market, mine is just fine vs $450 for a new one.

Re: reviving old seacraft (propeller question)
 

It's been a while, but it's taken me this long to get the old Merc 200 running right (new stator, trigger, switchboxes, rectifier, a bunch of tuning, timing, syncing, and a set of much nicer carbs off of Ebay)!
For those who recommended the 19 pitch prop...right on the money. 43/44 knots @ 5500. I went with an inexpensive Michigan Wheel aluminum 3 blade.
Now my next issue is the chine walking. The cavitation plate has one of those doelfins on it. Good or bad? It seems overkill as the boat jumps on plane with the engine trimmed down. Is there anything I can do besides trim tabs to help the boat ride level? It seems to want to fall off onto its port side a lot. Thanks for your input.

Re: reviving old seacraft (propeller question)
 

Bits . . . lose that prop. Put on a Mercury Mirage "Plus" 19p or 17P. That will fix the light bow problem. I don't know what the deal is with some of the michigan props . . . they give these seacrafts really squirrelly handling problems. I've been through this before with my boat with the same motor. I also liked the Highfive, but the cruise and top speed was not as good as the mirage plus . . . a fun prop none the less. You can find them on ebay frequently for under $200.

As far as having a level ride . . . you can try to pull of the doelfins and adjust the zinc trim tab on the lower unit. I have a very small low profile one. I honestly think the prop will go a LONG way toward fixing your problems.

Re: reviving old seacraft (propeller question)
 

Tim is right, the prop is the place to start. Look on ebay. For example, a 19" Mirage Plus auction ended yesterday at under $200 on ebay.

Bitsamonkey, aQuestion: If you are using a steering cable and not hydraulic steering, can you achieve neutral steering pressure at cruise? By this I mean that, at cruise rpm in flat water, the boat does not want to turn left or right. Many times a percieved tendency to "fall off" to one side or the other is caused by a misaligned torque tab, or the wrong torque tab, especially with Mercurys, for some reason.

With different types of props sometimes you need to change the torque tab. Running a Mirage+ or PowerTech Offshore usually requires a long/deep torque tab that is offset to the rear in order to achieve neutral steering torque over more than a very small rpm band.