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-   -   20' SeaCraft - better w/ or w/o a bracket ??? (http://www.classicseacraft.com/community/showthread.php?t=18373)

Bushwacker 10-18-2007 12:21 AM

Re: 20' SeaCraft - better w/ or w/o a bracket ???
 
JohnB nailed the key issue regarding brackets - balance! When the 20' hull was designed in the 60's, the biggest OB's were the I-6 Merc & V-4 OMC's that weighed about 275-300 lbs. With that setup, the gas tank was centered right on the cg so trim didn't change with fuel load. I ran my Seafari for over 30 years with a 115 V-4; it cruised easily at about 20 kts with a heavy, 2-weeks-in-the-Bahamas type load, rode well and always felt well balanced. At the Anclote Key gathering in March, I asked Carl Moesly about the design parameters on the 20, and he said it was designed primarily for inshore use, unlike the 21, which was designed for offshore use (and racing!) with much less dynamic lift, so it would cut thru big seas w/o becoming airborne. The relatively light weight and low deadrise of the 20 shows up in head seas at or above about 3', because it will get airborne pretty easy if you run much over 20 kts. With a light motor and a lot of gear in the cabin, I found I could trim motor and tabs down and plane at 12-13 kts and ride very comfortably (sitting down) in 4 and even 5' head seas provided period was about 6 sec or more. This is a big deal when you're running 165 nm to the Abaco's! The only thing I didn't like was that open transom in big following seas! On my first (of 6) trip across the Gulf stream, we had winds of only 10 kts, but it clocked from NW->N->NE! We were about 30 miles out (middle of stream, max current) when wind was N - seas were 6-8' with an occasional breaker, and seemed to be only about 40-50' apart, steep enough that I was worried about stuffing the bow into the back of a big one and pitchpoling! I guarantee that most folks in those conditions will "get religion" if they haven't already done so! (MORAL: if there is ANY wind out of ANY northern quadrant, stay the hell out of the Gulf Stream!!)

Sure wished I had a solid transom at that time, so when I finally repowered last year, I had the transom closed in, picked bracket with most flotation and lightest & quietest motor I could find, the V-6 150(165!) E-Tec at 427 lbs. I probably would have bought the V-4 115(125) which is about 50 lbs lighter but they were not yet in production. Waterline is within about an inch of original and boat is still self bailing, so the big bracket maintains static balance provided you don't go nuts with engine weight. I believe the Seafari has more weight forward than the cc, so it probably will handle a bracket better than a cc also. When you're up on plane however, bracket flotation is gone and the boat KNOWS there is a bunch more weight on it's ass, located 30" further aft! I believe this tends to hurt the ride a little, but you can compensate with a good stern lifting prop. A 4 blade prop was a big improvement over 3B. The bracket allows you to raise motor a lot (My cav plate is about 4.5" above keel) and is probably worth 2-3 mph in top end. I've seen almost 50 mph which seems to be pretty good for a 150 on the 20' hull, although I care about ride much more than speed. It WILL start to porpoise if motor is trimmed out more than about 60% (0=full down, 100=full up). This condition is most efficiently corrected by changing thrust angle (motor trim); trim tabs will also do it, but they add drag as well as lift, so use power trim to change running angle and use the tabs for side-to-side balance! Just my .02 FWIW. Denny

Bigshrimpin 10-18-2007 03:57 AM

Re: 20' SeaCraft - better w/ or w/o a bracket ???
 
You can see how much higher out of the water a 25" motor sits

http://www.casdvm.com/photos/Tims%20...t/DSCN7007.JPG

I had this boat backing up into white caps along side the berkeley pier in nasty afternoon SF Bay winds rescuing a kayaker and his river kayak (upside down full of water). There's no way I could have done that with my 20 MA and open transom.

The seafari with the bracket doesn't corner at high speeds like the MA and the reverse handling isn't as good, but I'm seriously considering filling in the transom on the MA and doing another bracket this winter.

zach 11-29-2007 06:04 PM

Re: 20' SeaCraft - better w/ or w/o a bracket ???
 
Quote:


Sure wished I had a solid transom at that time, so when I finally repowered last year, I had the transom closed in, picked bracket with most flotation and lightest & quietest motor I could find, the V-6 150(165!) E-Tec at 427 lbs. I probably would have bought the V-4 115(125) which is about 50 lbs lighter but they were not yet in production. Waterline is within about an inch of original and boat is still self bailing, so the big bracket maintains static balance provided you don't go nuts with engine weight. I believe the Seafari has more weight forward than the cc, so it probably will handle a bracket better than a cc also. When you're up on plane however, bracket flotation is gone and the boat KNOWS there is a bunch more weight on it's ass, located 30" further aft! I believe this tends to hurt the ride a little, but you can compensate with a good stern lifting prop. A 4 blade prop was a big improvement over 3B. The bracket allows you to raise motor a lot (My cav plate is about 4.5" above keel) and is probably worth 2-3 mph in top end. I've seen almost 50 mph which seems to be pretty good for a 150 on the 20' hull, although I care about ride much more than speed. It WILL start to porpoise if motor is trimmed out more than about 60% (0=full down, 100=full up). This condition is most efficiently corrected by changing thrust angle (motor trim); trim tabs will also do it, but they add drag as well as lift, so use power trim to change running angle and use the tabs for side-to-side balance! Just my .02 FWIW. Denny

Can anyone give a similar description to bushwacker's about their experience with a floatation bracket on a 20SF (the center console)? I am redoing my '72 and have seriously contemplated putting a bracket with a floatation chamber on. I plan on moving the fuel tank forward and batteries under the console to compensate for the extra weight on the transom. Any thoughts are greatly appreciated.

CaptLloyd 12-01-2007 02:02 PM

Re: 20' SeaCraft - better w/ or w/o a bracket ???
 
I added a bracket to my '73 20cc in 2003, I love having the bracket, the room I gained, and I have never had any worries of water over the transom whether running, drifting, or backing down. And having the full swim platform is fantastic for diving/swimminmg

But I would do a few things different. The B-Bracket I used doesn't have enough floatation IMO. Also it has a 30" set back, I could have used a 28" set back (the set back allows enough room for the motor to tilt all the up without the cowling touching the closed in transom) With my Suzuki 140, I could have used the 28", and when moving that kind of wieght farther back, every inch counts.

On plane, my boat would porpoise if the motor wasn't trimmed way down and/or the trim tabs way down. I added 150 lbs of lead to the forward compartment (I guess this makes my boat a "Pig Boat")and moved my batteries forward, this helped the porpoise problem as well as the static trim.

I like Bushwackers 4 blade stern lifting prop suggestion, I will try that when I get a chance. I'm also considering building a fiberglass shell to attach around the B-Bracket to add floation to the stern, then I may be able to remove some of the lead.

I would say use a Hermco bracket, keep wieght as far forward as you can, and play with different props. Like mentioned before, the 20cc was not originally designed to have the motor set that far back, so you will have to do some tweeking, but for what you gain with the bracket, I feel its worth it! Good luck!

Lloyd

JohnB 12-01-2007 02:32 PM

Re: 20' SeaCraft - better w/ or w/o a bracket ???
 
I have a question for the guys that have brackets on their boats. If you have a hermco bracket, is it contacting the water when you on plane? If it is, that is more wet area, and your loosing effieciency, and defeating one of the reasons to have a bracket in the first place???

I thought one of the big ideas of a bracket is you could take a 23' boat, turn it into a 27', without increasing the wet area/aka drag. This allows you to put big motors on the back and have extra floatation when at rest when you need it, and less drag/per foot on the hull when under way. If the bracket is dry when your running, it adds zero floatation. I am putting an armstrong on mine, and looking at it, it appears that it will not contact the water when on plane, and the floatation chamber only adds floatation when at rest.
Am I missing something?

Bushwacker 12-01-2007 02:53 PM

Re: 20' SeaCraft - better w/ or w/o a bracket ???
 
John - the Hermco bracket is completely out of the water when you're on plane, so doesn't add any drag. It probably reduces drag because you can mount the motor higher. Of course the flotation also goes away on plane. Like I said earlier, the boat knows you've changed the weight distribution, so beware of hanging a heavy motor on a bracket. I didn't notice any porpoising until I raised the motor 2" from where Don Herman originally mounted it, and I considered that a good trade for the extra performance I got. Even now it doesn't porpoise until motor is trimmed out to about 60-65% of max (where 0% is full down), so not a big deal. This may be the result of the SeaFari being better balanced than a cc (more weight forward) to begin with.

askipper3 12-01-2007 02:55 PM

Re: 20' SeaCraft - better w/ or w/o a bracket ???
 
Transom angle is 16 degree's right?

im want to put one on mine too

PressureDrop 12-01-2007 02:59 PM

Re: 20' SeaCraft - better w/ or w/o a bracket ???
 
CaptLloyd - What size/shape prop are you running and what speeds are you getting at certian revs, at least cruise and top end? i have the same set up (140 johnnyzuk on bracket) on my seafari (with bottom paint and big ass top) and the fastest ive seen is 37mph but thats going with the current, i can cruise at 29 at 4200 and wide-o about 35mph on a good day, i think i may need to adujst my cables though, but please post your #'s im very iterested,

Thank
Ben

JohnB 12-01-2007 03:08 PM

Re: 20' SeaCraft - better w/ or w/o a bracket ???
 
bushwacker,
Thanks for the reply. I think the boat manufactures figured this out when they started putting brackets on new boats, and adjusted the center of balance forward. I think they move the gas tank forward, and I also noticed the the consoles are starting to move forward too. I do think the Sceptre/Safaries fair better from this modification than the CC's from a balance perspective. I can't wait to splash mine and see what the differences are. I left my gas tank in the same place, I was already bow heavy with the top on my boat. It also had 2 "pig iron" balast weights in the back that I removed. I think they wieghed about twice what the bracket does, so it should be neutral.

76Red18 12-01-2007 04:18 PM

Re: 20' SeaCraft - better w/ or w/o a bracket ???
 
I think the big tops hold us back. My 18 with a 150 only sees 42 with everything else being correct. 15 1/4 x 19 prop. When I first tested it there was no top. It seemed a lot faster but I was so excited I forgot to look at the gps.


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