Shamrock's Performance

Nomad Willy · Sep 16, 2012

Lots of undesirable stuff going on.

Highly loaded prop set at an angle to push the boat to one side and prop walk to push the boat to the same side and a small rudder to control the boat's direction. Nothing is offered for directional stability. The rudder is offered to that end but it's possibly/probably already over loaded. A small keel approximately on CG giving lateral stability but no directional stability. The rudder correcting all these stray forces creates more drag than it should and all this together may explain the boats moderate performance. Was there ever an OB version or do you know of any conversions?

As to the flat turns My Easy Rider turned absolutely flat before I put on the cabin. Then it banked noticeably .. not a lot but more than a little. I concluded that raising the CG was responsible so perhaps the low CG of the Shamrock is the reason for the flat turns. The low CG is probably not exactly a bad thing unless you trip a chine and flip.

psneeld I think a lot can be learned from observing and evaluating. Wrong conclusions can be made but as the old saying goes one will learn from their mistakes. So I'm going to keep on look'in, think'in and evaluating.

Moonstruck · Sep 16, 2012

For you guys not familiar with the shallow waters of SW Florida, the Shamrock keel drive was designed to protect the running gear from groundings. Down there it is truly not a question of if, but when you will run aground. It was a compromise design that I don't think worked well in all areas. Pine Island Sound, Lemon Bay, Charlotte Harbor, and the areas around Naples, Ft. Myers, and Marco certainly have their trouble spots.

My Black Fin being a heavy, deep Vee, single screw draws an inordinate amount of water. It is an offshore boat not well suited for the above waters. I have had it there quite a bit, but not without extreme care. Compared to the Shamrock the Black Fin will ride in the same chop like it is on shock absorbers. No pounding whatsoever.

twiisted71 · Sep 16, 2012

There was exactly 1 OB model/prototype. I don't remember much said about it other than the cost of an OB large enough to match the V8 and it changed the "feel" the were looking for.
As far as propwalk: that would have been a nice complication to have (atleast I could have used it to my advantage). They just reversed and the bow swung which ever way the wind took it. The 26 with the cabin was truly the most aggravating boat to back into a slip I've ever owned, unless it was dead calm. Then she'd make you look like an ace!
Like I said before, and PSneeld should back this up, tracking was one area the thing excelled at. It was sort of like a sailboat in that regard even to the point that it would feel like it wanted to round-up when the wake from a boat overtaking you hit.

Yes there were a lot of areas I would like to have improved upon. I wanted to put in a tunnel and modify the keel accordingly. This would have greatly improved the prop angle and should have resulted in better efficiency/speed/draft. They made a half-hearted attempt at this on the later SPII versions and did away with the keel altogether and increased the beam 6". I come from a commercial fishing background in S.La. We built our tunnels deep enough so that atleast 1/2 the prop was above the bottom (this was needed in order to be able to get into the shallow bays when shrimping). Our raw water intakes were in the top of the tunnels as it was normal for the boat to be sliding along the bottom. It was a fine line to walk because if even 1/2" was above the waterline the prop would catch air in reverse=useless.
The Shamrock's rudder shape always puzzled me. They had fairly decent depth on the early boats (later ones were shorter) but instead of a flag shape they used a spade profile. Slow single screw boats need RUDDERS!

twiisted71 · Sep 16, 2012

MS Is the blackfin the same hull as the Bertram? I love watching those boats run in 3'-4'ers. Its almost like they are riding swells instead of waves.

Have you seen a Shamrock 31 GrandSlam? They have the deep deadrise and usually a pair of 6BT Cummins, supposedly they ride like Cadillacs due to all that weight and deepVee in a relatively small footprint. I've heard the even made a 24' version of it.

Art · Sep 16, 2012

Eric Great to learn your inputs...

IMHO, from personal study and years of hands-on air and water foil tests:

Surface pressures, friction, and directional dynamics of the surface to surface actions for fast and faster moving solid objects traveling over/slightly-through water are directly affected by and proportional to water composition as well as movement energy (force) applied-to, angle of the plane, contour of, surface texture of, and weight distributions of a solid object. Not unlike a skipping stone’s capabilities... craft moving over/through water, in order to attain high efficiency, must have the afore mentioned items symbiotically functioning in their best physics applications to enable best accomplishment toward each other’s needs.

Water test tanks for hull designs are very similar to wind test tunnels for plane designs... in that... although one medium is liquid and the other a gas the combined static and dynamic reactions to any solid objects’ material, shape, weight, form and force-applied are surprising similar to achieve high efficiency for movement in/through/over either medium. A light weight Frisbee’s airfoil actions are surprisingly similar to a well chosen light weight skipping stone design’s water foil actions. Of course due to looser molecular stance and lesser surface friction developed than water air foil solid products can move faster/further with less applied energy. But, solid objects’ water foil capabilities are the focus here! Also, not too unlike reduced friction reactions accomplished via stepping bottom designs in high speed boats there is a certain increased efficiency level that can be realized by a specific stippling design on bottom surface... that upon reaching certain speeds will notably further reduce surface area contact for more friction reductions.

Art

Nomad Willy · Sep 16, 2012

Art,
That's deeper than my stuff.
I'd love to have a test tank but I'd need a crew of model builders to keep up w my wandering curiosity and ideas.
My experience w aviation has opened doors to marine understandings that I otherwise would'nt have.
Twist,
With the skinny boating Don's talk'in about seems to me the OB would be ideal. I suspect the Shamrock market may have been an extension of an attitude by the builder about OBs ... Naw I wouldn't have one of those things. OBs are for old ladies. Some people like the big guns noise. Kinda like low rpm in a trawler that serves no purpose. But I sure like walk'in around the back of my 455 Buick and listening to the pipes. Music.

Moonstruck · Sep 16, 2012

twiisted71 said:
MS Is the blackfin the same hull as the Bertram? I love watching those boats run in 3'-4'ers. Its almost like they are riding swells instead of waves.

Have you seen a Shamrock 31 GrandSlam? They have the deep deadrise and usually a pair of 6BT Cummins, supposedly they ride like Cadillacs due to all that weight and deepVee in a relatively small footprint. I've heard the even made a 24' version of it.

Right Twisted. The Black Fin was a knock off of the Bertram hull design. My 25' has an 8' beam. So it is narrow and slippery. She rides low in the water until the bow is brought up on plane. One guy said he had never understood that boat until he saw me busting out Perdido Pass through 6' breakers.

Mine is a 1978 that I have had for years and years. We have restored it twice. The big Cat engine gives it plenty of prop walk in reverse. However she is a sweet handler and rider. My wife could sleep while we were running back in from 45 miles offshore through 4 footers. She ran the boat for 100 miles with 4' following seas to Horn Island while sitting up on the leaning post. That boat loves a following sea. Tracks like it is on rails.

I have seen the 31 Shamrock, but never run one. I did not know that is was considered a deep Vee.

twiisted71 · Sep 16, 2012

Moonstruck said:
I did not know that is was considered a deep Vee.

I don't know if there is a definitive degree which determines "deep" vee but its way more than a standard Shamrock.

https://picasaweb.google.com/114115...rYvpuhpAE&feat=directlink#5759930163212018514

MB supposedly they were built to appeal to people who wanted a boat like work truck. No frills, dead solid reliable, easy to maintain, take it out and use no matter the conditions, hit it with a waterhose when done.
As happens with many brands, the originator sold out (but the purchaser didn't have love for them) and it wound up in the Brunswick umbrella for a while, they sold when they realized that tomake a boat like that wasn't profitable. It ended in N.C. with the guy who owns Palmer Marine (I think) supposedly he tried to build it like most new boats and quality suffered and it soured the name a bit then he walked away and left the whole shootin' match and the factory was seized but not before a lot of the molds had been left in the weather and ruined.

On a side note the original designer now makes bodies for ultralight helicopters!

Moonstruck · Sep 16, 2012

twiisted71 said:
I don't know if there is a definitive degree which determines "deep" vee but its way more than a standard Shamrock.

https://picasaweb.google.com/114115...rYvpuhpAE&feat=directlink#5759930163212018514

The Black Fin bottom is about a 24 degree V. My Sabre bottom is a 16 degree V. It takes a lot of power to get a deep V hull on plane. However, the ride is superb. They will take seas from any angle but beam. It is not difficult the alter course enough to make that comfortable.

The picture of the Shamrock V looks like 14 to 16 degrees. That is a pretty good compromise, but still won't ride like a Bertram.

twiisted71 · Sep 16, 2012

Moonstruck said:
That is a pretty good compromise, but still won't ride like a Bertram.

pound for pound I don't think there are very many that even come close

Here's a link to the 31GS 19* deadrise

http://www.powerboatguide.com/Free_Access_files/Shamrock 31 Grand Slam.pdf

psneeld · Sep 16, 2012

manyboats said:
Art,
That's deeper than my stuff.
I'd love to have a test tank but I'd need a crew of model builders to keep up w my wandering curiosity and ideas.
My experience w aviation has opened doors to marine understandings that I otherwise would'nt have.
Twist,
With the skinny boating Don's talk'in about seems to me the OB would be ideal. I suspect the Shamrock market may have been an extension of an attitude by the builder about OBs ... Naw I wouldn't have one of those things. OBs are for old ladies. Some people like the big guns noise. Kinda like low rpm in a trawler that serves no purpose. But I sure like walk'in around the back of my 455 Buick and listening to the pipes. Music.

Your guess is way off base... I take a Shamrock where PWCs fear to tread because of the full keel and dredging ability of an inboard prop.

Your theories are textbook and have little to do with the real use of many boats from what I have been reading.....the design of a Shamrock is about as far from an outboard powered boat as you can get except for the early model kit lobster boats designed for outboards that finally wised up and lost the keels.

It is what it is...it was designed that way as described by those familiar with them and that's where they stayed a few years till the outboard revolution sent the older style hull designs into a tailspin for marketing and the "offshore" fishing rage....ala the triple outboard brigade....

Nomad Willy · Sep 16, 2012

psneeld,
Your response is 100% in character w all your posts that I can remember.
Getting easier to read though as the surprise is not there at all now.
Your intent is obvious to me but of more interest to you should be that it's very evident to everyone else as well.
You're quite knowledgable and it would be nice if you could be a bit more friendly and less critical.

psneeld · Sep 16, 2012

manyboats said:
psneeld,
Your response is 100% in character w all your posts that I can remember.
Getting easier to read though as the surprise is not there at all now.
Your intent is obvious to me but of more interest to you should be that it's very evident to everyone else as well.
You're quite knowledgable and it would be nice if you could be a bit more friendly and less critical.

I just have 2 questions...

Have you ever handled a Shamrock?

If the answer to question #1 was no...why would you start a thread discussing a bunch of incorrect hypothetical assumptions about the design???? Then complain when someone called you out on it???? :socool:

And I thought skin was thicker in AK.... :rofl:

Giggitoni · Sep 16, 2012

That's three questions.

Tom.B · Sep 16, 2012

You guys need to settle down and be civil, please.

psneeld · Sep 16, 2012

GonzoF1 said:
You guys need to settle down and be civil, please.

Without inflection...written word can be taken a lot of ways...being forthright can seem uncivil to some....but read the words...there is meanness...just a point of view in them...

Plenty of people disagree with me all the time on this forum...I just post back or ignore it...calling someone out for what they post if not personal or vulgar shows me something that I knew all along.

psneeld · Sep 16, 2012

Giggitoni said:
That's three questions.

Sorry...I too make mistakes and get carried away.... :facepalm:

CPseudonym · Sep 16, 2012

Never a bad idea

twiisted71 · Sep 16, 2012

Shamrock's are hard to comprehend until you've spent considerable time with one. You'll develop a love/hate relationship but you'll respect their capabilities nonetheless. If I had to run mine as a job (like PS) I'd probably have fallen more on the hate side as well. I was able to run mine as it was designed, at a leisurely pace. There are many threads about trying to make them what they are not on "Fishtheclassic". The only widely agreed upon improvement across the board is spray rails. Other than that, if you want plush, get a bowrider: speed, get a contender: want an economical to run/maintain, easy to repair boat that can take way more than 99% of boaters wanna try,.........enjoy your Shamrock!

psneeld · Sep 16, 2012

twiisted71 said:
Shamrock's are hard to comprehend until you've spent considerable time with one. You'll develop a love/hate relationship but you'll respect their capabilities nonetheless. If I had to run mine as a job (like PS) I'd probably have fallen more on the hate side as well. I was able to run mine as it was designed, at a leisurely pace. There are many threads about trying to make them what they are not on "Fishtheclassic". The only widely agreed upon improvement across the board is spray rails. Other than that, if you want plush, get a bowrider: speed, get a contender: want an economical to run/maintain, easy to repair boat that can take way more than 99% of boaters wanna try,.........enjoy your Shamrock!

Not leaning to the hate side...it does the job I need it to do better than anything except maybe a custom knockoff...

I just think of it as the ultimate compromise boat...which for a utility craft is probably the best thing it can be!!!

Shamrock's Performance

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