20ft SeaCraft With Twin V4's??? Just Thinking OL..

[strick]

Heres a couple pics of my first test drive with the bracket and a short clip of Capt Chuck's boat getting it on. Compare the running surfaces of the bracked boat vs the non bracketed boat. Both boats are at cruising speed 30 plus MPH.

http://www.casdvm.com/photos/gettin%20it%20on.mpg





Strick

[Fr. Frank]

Dunk is right, and so is Strick. It depends upon the hull, and especially on the amount of rocker in the hull. In a previous life, I spent some time as a test pilot (strange name, that) for Wellcraft, testing engine and propeller combinations for new boats, or new factory power set-ups for renewed models.
For instance, Wellcraft chose NOT to make a 19' bracketed OB version of the Scarab hull after testing showed that that configuration porpoised continually without putting K-planes down in the water at 10+ degrees at all times - not enough hull length to rocker.
Here's a rule of thumb we came up with, which Wellcraft follows to this day. If you set the hull on the ground, balanced from side to side with the keel line at the transom touching the ground, at 45% of the vessel LOA the hull must be in contact with the ground. In other words, there must be no appreciable hull rocker in the aft 45% of the boat in order to put a bracket on the hull.
The last Wellcraft production hull to violate this rule was the 1990 26' Scarab OB center console. Rigged with a B-bracket for twins, it came factory equipped with either twin Yam 130's, or twin Merc 115's. On plane, the boat porpoised, always. Testing w/ V6 OB engines showed the aft CG made it worse. When we tested the same hull with transom mounted engines, the problem was greatly reduced. The hull had a 37% rocker point.
I have seen many 20 SeaCrafts with bracketed OB's, and all seem to run fine. A 20' Seacraft has a rocker point GREATER than 60%. So does a 23".
On the other hand, my 20' Seafari seems to like it's transom mounted V6 Merc [img]/images/graemlins/cool.gif[/img]

[ocuyler]

Wow! That's experience! What a great site!

[strick]

Thanks for the info Frank. It's nice to have a scientific approach to things. I wonder if anyone has ever done a study and published a paper on the subject of adding a brackets.

Strick

strick

[Capt Chuck]

I would have to disagree with several statements here
A 30" setback of the engine does not change the center of gravity 30 inches The amount of buoyancy in the bracket coupled with the weight of the engine / engines also have to balance, thus the "wave cutting part of the deep vee" hull will not be changed. As a matter of fact, the 410 lbs of floatation in the Potter Bracket Eliminates the typical "Stern-Squat" and decreases the running and the at-rest draft by 3" or 4" [img]/images/graemlins/shocked.gif[/img] The boat will be drier ("NO"Spray rails),Decreased Fuel Consumption and increased Top End and Crusing Speeds with the same HP will be realized. No water into the cockpit when backing down, reduced engine noise and reduction of prop ventilation during tight turns will also be noticed [img]/images/graemlins/smile.gif[/img]

On a 20 footer, the bracket will reduce sliding of the hull. You might experience a slight tendency to porpise at a higher speed but trim tabs will correct that problem real fast. The chance of chine walking with a higher HP motor would be reduced. Added weight by a larger fuel tank and/or moving the twin batteries up forward also must be considered.

All these benefits along with the added cockpit space sold me on bracketing my SeaCraft. You can follow along with my transom transformation on another thread. OK I'm off my

[cSickNick]

Guys, this is a very interesting post! As Frank says, I agree that Dunk and Strick are right on!
But, I am hoping I can change Dunks "47 years on the water" opinion on "My next rule is nothing under 23ft get's a bracket" on the 20' Seacraft based on my needs and these facts;
- Franks Wellcraft test pilot info "In other words, there must be no appreciable hull rocker in the aft 45% of the boat in order to put a bracket on the hull." "A 20' Seacraft has a rocker point GREATER than 60%"
- Use a Seamark Bracket, from Hermco.net "Conceived and designed by "Bill Potter" a renowned boat builder and former company owner of Seacraft offshore fishing boats (1968 - 1980) the Seamark Bracket is simply the best way to get your boat up to speed, safety and usability!"
- Full transom, love the look of a full transom inside and out. Not for "Notched Transom" fear. I feel that is over rated as Dunk states above.
- 20' Seacraft cuddy fits my fishing/boating needs and budget for a long time!
So Dunk, can we change your mind based on this. This is what all cuddy's guys are talking about;
I can only take an educated guess that Strick is going to duplicate one! [img]/images/graemlins/grin.gif[/img]
Thanks Nick!!

[red20]

wow what a learning experience. I say no bracket on a 20. Back to the original question abot twins on a 20'. Last year, give or take a year, there was a 1984 20' w/ twin 115 hp mercs in the trader. Seemed to use the standard cut out? If you do it post some pics. [img]/images/graemlins/smile.gif[/img]

[Finster]

Red20, thats seems like a lot of weight for a 20 on a stock transom. Df115's are 385 lbs. and the newer 2 strokes are not that much lighter. I could see possibly doing it with older/lighter 2 strokes, if thats your thing. But in my opinion if you sit 700+lbs. on a stock 20, your gonna sink.

Back to the 45% hull thing. I agree with Fr Frank on that. I have a 15 whaler dauntless, and that boat can't help but porpoise. Though my feeling would be, if you put say a hermco bracket on, which is more or less an extention of the hull it would give greater than 45% there for eliminating the problem. But I'm not going to try it.

[eggsuckindog]

Dunk I wouldn't put twins on a 20, my 23 ran so much better with the old V8 Rude than the twin 150's it wasn't even the same boat. My theory is with the VDH the hull will pivot on the the center deadrise and get up, with the twins your trimmming it on the outer deadrise, it really wasn't the same boat and since I had an extra hole I had them stick a 55MPH speedo in, not enough, would go all the way around to the 0 peg. 1978 23 Sceptre V8 Rude, 60 should easy with a big single.