18 2+3 X Dimension Comparison

[Rootsy]

Well kids, it is time to cut the hole in the "Red Mistress". I have conferred with all do the donzi gods and no one has a "Difinitive" answer on exactly where to put the hole... sure there are theories but a definite location is very ambiguous.

But no matter... i have taken all information suggested, given and engrained into me and i have compiled it... mulled it over and looked at the path i want to go with drivetrain... At this time it's going to be a Merc Bravo... at some point i was figuring on a 2" IMCO... parts are expensive and i am not independently wealthy so future "experimentation" would depend on the generosity of my fellow donzi owners in loaning me "test" parts... If i can i'd actually love to just run a bravo.. add a nosecone if required and forget the shortie... and from looking at it this is quite possible IMO... IF i have the balls to get aggressive enough with the crankshaft location...

Standard X dim (location of the engine crankshaft C/L) from mercruiser is stated as 14 1/2 inches from a horizontal datum line located 1 inch above the TRUE bottom of the boat... True bottom being the theoretical sharp of the V (or vertex in mathematical terms).

I knwo.. FOR A FACT... and i don't care who disputes it... that 3" UP on the Propshaft location on an 18, round keel... works without issue and makes for an all around better handling boat... this is achieved with an alpha SS and though some aspect ratio and drive case design and hydrodynamics may come into play, regardless, it works slick as poop... ask DougL about his 18... ask me about my 16... ask a few others running SS's on 16 and 18's...

Now my dilema... my 18, being a "Barrelback" has a sharp V... no radiused keel... there is a 1 inch Radius on the keel to knock the sharp off but that is it.. btw, the 16 and 18 round bottom formula says 1" of radius per foot of boat.. so on an 18.. that'd be 18 inches of radius on the keel.

as you will see in the diagrams that i have prepared for you is that a few items become clear... #1 is that in all regards the propshaft is CLOSER to the keel on the sharp V boat for a GIVEN propshaft location. #2 is that area of coverage for a prop diameter vs hull increases quickly as you raise the X on a round keel boat... on a Sharp V hull it is slower on increase but diverges as you go up from the round keel area and it starts POSITIVE whereas the round keel begins with negative coverage... as example.. round keel 18, with a 14 3/4 diam prop with a +3 X Dim has a coverage of 13 1/2 square inches... @ 3 inches on a sharp V with the same prop you are at almost 21 square inches...

my observations tell me that a sharp keel boat should not require an as aggressive X dim (speaking of propshaft relative to keel now) as a round keel boat to achieve similar performance...

on the sharp keel boat you have a fully straked hull and that forces the nose downward more aggressively than a round keel short strake hull.. eventhough the round keel acts as a semi-pad... this is easily seen by comments from other barrelback owners...

the BIG UNKNOWN for me is that I AM going to remove approx 8 - 12 inches of inner strake... this is a given there is no changing my mind.. it is set in stone, err fibeglass :)

so please study the attached photos... and let me know your thoughts and views...

[MOP]

Jamie I read a post on OSO a little while back about the X on round "vs" sharp keel, the just of it was the round keel alows a higher X the the sharp keel. I will give a shot at finding the post it may be of help with your thoughts.

[penbroke]

How about this: Calculate the area where the circle of the prop overlaps the hull at the 3" raised X on the round bottom. This would be the area of the prop that would be exposed to air if the water didn't rise after the boat passed. Make the area of the overlap the same on the sharp bottom. Where does the X end up? Just thinking outloud...

Frank
When did we become "kids" anyway?:smash:

[Rootsy]

How about this: Calculate the area where the circle of the prop overlaps the hull at the 3" raised X on the round bottom. This would be the area of the prop that would be exposed to air if the water didn't rise after the boat passed. Make the area of the overlap the same on the sharp bottom. Where does the X end up? Just thinking outloud...
Frank
When did we become "kids" anyway?:smash:
i did that, of course frank :) 3 inches on the round bottom is 13 1/2 in^2... 1 1/2 up on the V bottom is 12.83 in^2
as it sits RIGHT NOW i am going to cut the hole at 14 1/2... because of the fact that i realize a shorter lever arm gives a better ride than raising the engine... so we'll run the bravo @ 6.5 below the transom installed @ 14 1/2 (vs 8 inches on a round bottom @ 14 1/2)... so essentially we're already 1.7 above the round bottom.. that is the amount of the truncation due to the radius vs sharp keel... a 2 inch shortie will be a gamble even @ 14 1/2 on whether or not i can even get it to hook up... might have to find a 1 inch IMCO....

[Lenny]

Jamie, the 14 1/2" centerline on the round keel boats IS measured off of the actual hull bottom from DONZI. Not that description you depicted in pic one that shows the bottom line below the tangible (touchable) bottom.

? ? ?

Am I missing something, other than the obvious stuff we all already know about ?

[Rootsy]

Jamie, the 14 1/2" centerline on the round keel boats IS measured off of the actual hull bottom from DONZI. Not that description you depicted in pic one that shows the bottom line below the tangible (touchable) bottom.
? ? ?
Am I missing something, other than the obvious stuff we all already know about ?

i've heard this before... but i have also measured my 16 and doug's 18... propshaft C/L to bottom... knowing the sterndrive length propshaft C/L to input shaft C/L... my drawing is perfectly ligit... i dont doubt that donzi has a templet to lay upon the hull to cut from but at one time i reckon someone did the math to make that templet off of that datum line... they may fudge it from time to time for customers but from my math... i know that what i drew is correct based upon ACTUAL measurements from my 97 16 and an 87 18. MY alpha GEN II was 8 inches from the tangent of the radius on keel to propshaft C/L... the Alpha SS was 5 inches... the smaller radius of the 16 accounts for the 1/4 inch or so difference between my boat and dougL's 18....

Round bottoms are one thing... we talk about chainging X dimensions on them all of the time... this is not a round bottom boat... and i just want to understand the differences in setting up a sharp keel vs a radius' keel hull... since so few of the sharp keels are around and not a WHOLE lot of people have done what this thread is discussing, getting information is difficult.. therefore we probably are gonna have to "THINK".... speculate and interpolate.

MP,

i agree... and i have the clearance... the whole shorter lever arm thing is what is getting me...

is there another 20 ft or less 24* true V (no pad) fully straked hull that runs 70+ out of the box with merc power (say 6.2 or scorpion) ?

[smokediver]

I hate to say the word ... baja has a sharp keel and i believe some of there older 20 models would run that fast with a big block ... the older hammer and sidewinder ...

[BigGrizzly]

Herwe is a though. Talk to Brownie, he was involved when the made the change. He told me the change was made because of the cornering difference in the two designs. Since you are removing 8-12 inchs of bottom strake it WILL have a softer re entry. This I know because we did it on John Fennemor's 18 In the late 1960's. HYe saw a Nova and wanted to do it. I think he did about 12 inches. With horse power you don't need the full length strakes. I don't remember myself but he sais it handled better and didnot "fall over" in turns as much as before and every thing else was the same. My suggestion Go with your theories and let it go! No one has ever done it so now one has the real answer. Everon said I couldn't close cooling a blower motor. they also said I had to run it without a T-stat. They also said I would never brake 80 mph. and a three blade would make my boat handle bad if I ever got there. Let me tell you "THEY" were wrong as you know. You have the knowlege, you have the ability, and you deffinatly have the drive. The only thing I can do is let you try any prop that I have or can get. If you can't come down here I'll go up there with 10 or so props to help out. Oh yes it is warmer here and we don't have to pull the bot to prop it we lift it on the Hydro Hoyst and your done. Go for it I'm on your side.

[Rootsy]

the hole is at 14 1/2.... just have to drill the holes for the studs and clean it up a bit... a real PITA to cut through that much glass and wood... sawzall and jigsaw blade eatin mofo...

i figure at 14 1/2 that A) i measured the engine and everything will clear the hatch... i go up an inch and it gets kinda close and i want to run all of the air cleaner err flame retarder that i can... B) the propshaft is already 1.6 inches closer to the bottom that on a round bottom boat at this height... C) i have a few folks out there that will let me "test" their imco shorties when the time comes and @ -2 inches that puts me 4.6 inches below the keel... which is getting pretty high... D) i wanted to keep the weight as close to the chine line as possible and i would rather shorten up the drive than just raise the engine...

so we'll see how it runs there... the lack fo strake is going to be an interesting twist... thanks for all of the replies

[Mr X]

Bone stock?.....CHICKEN!! http://www.clicksmilies.com/s0105/tiere/animal-smiley-071.gif

Just kidding Jamie......

[Cuda]

You lost me when you got to horizontal datum line . :)

[Kirbyvv]

Rootsy, check with Scott Pearson, he put a merc stern drive on a barrel back.

[Rootsy]

Rootsy, check with Scott Pearson, he put a merc stern drive on a barrel back.

+ 1 1/2 i do believe

[Lenny]

...as did Chris Allard

[Rootsy]

well mattyboy is a true craftsman... the transom is EXACTLY 2 inches thick... the wood on the inside is flat as a pancake and it's all tight as a drum... he was the one sanding the transom wood before installation ;)
woo hooo the transom assembly fits like a glove... tight as a whistle to the back and the inside... :)
next we'll see if the engine fits....

[Ricardo Grande]

well mattyboy is a true craftsman... the transom is EXACTLY 2 inches thick...


So let me get this straight, Mattyboy drove 13 hours to help someone he'd NEVER met.....someone that he had made friends with on this site?

How can that be? I thought



"many of Matty's negative attitude posts trying to make me or others feel that they're unwelcomed when he didn't like the topic, but obviously I still drop by here because thats just the way he is with his written word and I chose not to post as often to avoid getting into a debate with every post knowing he's going to drop some sarcasm."

[boxy]

So let me get this straight, Mattyboy drove 13 hours to help someone he'd NEVER met.....someone that he had made friends with on this site?


Yeah he's a dink like that........ :D

[BigGrizzly]

You have to understand Matty. He is a true craftsman, and like me has a low tollerance for incompitence. Being from the North East, like me, he is sarcastic like me. Up there we are mostlu like that no harm ment it is just the way it is! You grow up like this and it seems normal. After working at Honda dealing with dealers and customers you learn to be cameilion, North East you talk one way south west another way. In my job fixing problems is what counted, the delivery makes or breaks the contact. Because of my delivery most of the North East dealers prefered me over the others. My bosses couldn't under stand it. "You are so personal and frank and sarcastic all at the same time".I was called unprofessional by one supervisor. I happened to mention this to a dealer and he and several others got together and wrote letters to our boss about the subject. Now when honda sent the dealer survey out the written response was amasing. Then she called me un orthodox. Oh well! BTW she has been removed from that position. Anyway I'm sure Matty didn't mean to offend you. To my Knowlege he has never refused to help anyone ever. I just felt I needed to explain this. I have only met him on the net. I do know that If I go up north next year and he Knows he will drive to Jersey just to meet me and talk.

[Patti]

What?

I'm from Brooklyn and i'm not sarcastic at *all* :wink:

[BigGrizzly]

I rest my case!! Regardless the North East and Jersey Shorer was a great place to grow up in when I a kid. Glad I'm from there.

[Rootsy]

btw,

i just wanted to add that once i rough cut out the hole with the sawzall... i put a 2 inch straight cutter in my router and "LIGHTY" went around the hole... if you had a "JIG" you'd use a ball bearing cutter that would ride on the jig and cut the hole nice and smooth... but i guess i got the job done the way i did it... just don't let me forget to "seal" the holes ;)

a big thank you to Greg for making a copy and mailing me the templete for the hole also :)

[farmer tx]

Most transoms are bevel cut around the tiller area, are you going to bevel it or do you have enough clearance as is?

[Rootsy]

Most transoms are bevel cut around the tiller area, are you going to bevel it or do you have enough clearance as is?

i still have to "trim" the inside :) you're on the ball ;)

engine fits... kinda... gonna have to reengineer the front motor mounts as the existing stringers are too high and won't quite allow the lower front motor mounts to clear. or i could use the Glenwood mount that you see.. but then there is no adjustment vertical adjustment and i have to mill a bit on it for bracketry... the alignment tool is in the coupler in these photos... and the rear motor mounts are set down on the transom assy... more or less.. one side of the motor is heaver than the other so it isn't quite "level" in the photos...

[TREYSTJOHN]

I noticed you're planning to remove 8" of the inner strakes. The stringers on a Vee hull in the engine compartment area sit on the inside flat area of those strakes. If you grind out the strakes from the outside, you will cut up into the base plywood of the stringers and lose width strenghth in the outer hull shell in this area. The only boat I have seen with this done to it, cracked lenghthwise at this area on both sides. If you are dead set on doing this, be prepared to cut the stringers up higher than the hull shell and build back down with a good epoxy resin with millled fibers mixed in to tie the shell back in.

Just my 2 cents

If you have any other structural question, we gutted my 1966 Vee down to the outer shell, so I may be able to help.

[Rootsy]

I noticed you're planning to remove 8" of the inner strakes. The stringers on a Vee hull in the engine compartment area sit on the inside flat area of those strakes. If you grind out the strakes from the outside, you will cut up into the base plywood of the stringers and lose width strenghth in the outer hull shell in this area. The only boat I have seen with this done to it, cracked lenghthwise at this area on both sides. If you are dead set on doing this, be prepared to cut the stringers up higher than the hull shell and build back down with a good epoxy resin with millled fibers mixed in to tie the shell back in.
Just my 2 cents
If you have any other structural question, we gutted my 1966 Vee down to the outer shell, so I may be able to help.

I'd love to see some photos of your 66 triple.. and see and hear what you have done to and with it.. as well as performance, etc...

as far as teh strakes.. yes some is coming off... yes i know that they were laid up in the mold.. then the stringers laid in... if you followed the red mistress thread at all you saw that i sistered 3/4 plywood to the existing stringers to bring the entire composite width to 1 1/2 inches for 8 feet of the boat... i did this because i was planning on the strake and it'd reenforce outward of the existing strake... so when i sawzall into the strake from the transom, forward maybe 10 - 12 inches... i will break out the router and pocket inward into the existing strake to remove it above the bottom.. and fill outward with glass and resin and taper the bottom outward and build it up with biaxial and triaxial stitchmat. hope that sets your mind at ease cause i keep telling myself it is gonna be juuuuuust fine :crossfing

please though, by all means... lets see your 66... lets hear what you've done and what you know about it... i am eager to learn from those who have gone before me. :)