Atkin "Ripalong"

[frank smith]

This hull form seams to be coming back in vogue. I dont know much about power hull forms, but i like the look of the lines . I am wondering if this hull form is still viable .

[PAR]

Well that's a rather old hull form and well before what we now understand about full plane hull forms. It has fairly well concave sections forward and the same of the waterlines aft. This makes for a slow boat.

It depends on what you want from this hull. It's got a fair bit of "suction" related to it, as it's a WW II era warped bottom. At relatively low speeds, she'll do fine, though once pushed past say about 27 - 28 MPH, she'll start to get pissy and squat on you. This type of hull form will max out at about 35 knots and you'll have to toss 225 - 250 HP at her to get there and she'll be pretty squirrelly at that speed, though only a 150 HP to see 27 which is quite respectable.

What are your intentions with this hull? Target speed? General conditions you expect her to meet?

[Mr Efficiency]

Jeepers, I'd have thought it a semi-displacement hull not intended for either high power or speeds. Trouble is they spend a lot of time pushing uphill when running with a following sea, which is not very efficient travel. Be pretty wet too, you'd think.

[michael pierzga]

Modern design thinking compliments Atkin.


The Atkin boat pictured is a beautiful example of a "low power " motorboat. She would be easily powered by a small friendly diesel and slip thru the water at moderate speed, on her lines, with minimum wake and fuss. Difficult to improve .

The attached pictures are for an ultra modern...low power...easily driven motorboat. You can see the design similarities. Volume forward, flat run aft.

If this is what your after, a low power boat, then Atkin drew great ones.

[troy2000]

Originally Posted by PAR

Well that's a rather old hull form and well before what we now understand about full plane hull forms. It has fairly well concave sections forward and the same of the waterlines aft. This makes for a slow boat.

It depends on what you want from this hull. It's got a fair bit of "suction" related to it, as it's a WW II era warped bottom. At relatively low speeds, she'll do fine, though once pushed past say about 27 - 28 MPH, she'll start to get pissy and squat on you. This type of hull form will max out at about 35 knots and you'll have to toss 225 - 250 HP at her to get there and she'll be pretty squirrelly at that speed, though only a 150 HP to see 27 which is quite respectable.

What are your intentions with this hull? Target speed? General conditions you expect her to meet?

Here's the Atkin & Co page, with William Atkin's original write-up.

http://www.boat-links.com/Atkinco/Cr.../Ripalong.html

Ripalong was designed to do 25 mph, with a 100 hp engine turning at 2400 rpm; which is a little below the point where you figure she would start misbehaving.

According to Atkin, "When under way at speeds over 15 miles an hour the first Rip does not stand up on her tail like so many of our fast runabouts, but rather rises for her full length and goes ahead with a very comfortable motion even in rough water."

Unfortunately, she also has her engine in the middle of the cabin....

[michael pierzga]

Oh and Frank. Im seeing more and more modern "ATKIN". type motorboats. I mean similar easily driven hull forms, moderate displacement, but ultra modern.." looks like she's going 100 knots" styling above. Im surprised when I see these modern boats out of the water and observe small displacement and a small drive train. A Thinking mans modern motorboat.

[PAR]

Michael you couldn't "recognize" an Atkins design if it fell from the sky and landed on your head. This design is one of Billy's old "pigs" by his own standards. He'd developed a much better understanding of the "hook" he and most from his generation where so fond of and entry sections in later designs. The "issues" with this design aren't difficult to see.

Mr. Efficiency, this is a classic powerboat shape of it's era and as Billy describes in the text, doesn't bow up at moderate speeds, but bodily rises. It's not a wet ride unless you're over driving her or the conditions warrant it.

As far as reasonably efficient, she's again not the better one of Billy's hull forms in this regard. The hull form is designed to run at about 25 MPH, but with 100 HP the first of these boats was doing 19.5 knots. It took 150 HP to get a tick over 21 knots (25 MPH) and this isn't especially efficient. This is because of the weight of the build and the power plants in the era she was designed. you have to remember 100 - 150 HP back then weighed 1,200 - 1,500 pounds and the hull had to not only have the volume for this weight, but the structure. I have a 1960 Chris Craft of larger general dimensions that will run 37 MPH on 185 HP. This is purely because the hull shape will permit her to "get up" and she isn't built to hold up a 3/4 ton power plant.

Lastly, because of the long hook (he got much better at the hook later in his career), he's limited her abilities over the mid 20 knot range (about 28 MPH) and the boat just becomes unstable. Look I'm not trying to be a dick, but either you are familiar with these old designs and their idiosyncrasies or you are not, which becomes quickly obvious. No one is designing boats with this type of hull form, nor have they for generations and understandably so.

[frank smith]

Par, and others , good stuff, I think there might be a market for this kind of boat concept .
Mid to upper 20's is a good average speed for many . Combined with comfort and easy going in moderately ruff seas, with say about a 50 mile max from home , on average .
A 4 cylinder turbo diesel for a motor . Not bad . But it needs a more modern hull form.
I like the round bilge , but a built in spray rail for a little extra lift. i still wouldn't want to loose efficiency and low fuel consumption for a little extra top end. I my experience,
mid 20's is a good average top cruise speed for this size boat . I dont see a max speed of over 35 as much use here.

What are the ups a down of a step in a hull like this? Would it be better to control attitude of the boat with trim tabs and forgo any hook in the bottom ?

[michael pierzga]

The Atkins yacht is perfectly designed. Trim tabs physically overcome weight, power and design inefficiency and consume energy to bring a vessel back on her lines to promote seaworthiness. . .

A vessel is divided into three sections. The bow deflects spray and works the vessel thru a seaway, the midsection absorbs the wave impact energy and the aft section is the speed..planning surface and steers the vessel. Atkins boat is superb and addresses each detail.

The power plant, the weight and the major longitudinal stiffness, pounding structure, of the vessel is amidships , the full bow section will be an effective sea keeper and the flat run aft will plane easily. The long flat keel and protected prop rudder will allow it to penetrate shallow water without fear and be easy to handle out of the water at a shipyard. .

If you want a fast vessel with a V8, look elsewhere...the vessel Ripalong is designed for low speed, low power, seakeeping and coastal enjoyment . Ripalong is a classic.

[tom28571]

Originally Posted by michael pierzga

The Atkins yacht is perfectly designed. Trim tabs physically overcome weight, power and design inefficiency and consume energy to bring a vessel back on her lines to promote seaworthiness. . .

If you want a fast vessel with a V8, look elsewhere...the vessel Ripalong is designed for low speed, low power, seakeeping and coastal enjoyment . Ripalong is a classic.

Well, maybe not perfect and his aft hull bottom already acts like a trim tab, although not adjustable.

A classic yes, but so is the '37 Cord and they don't make them anymore either.

[PAR]

Michael, why is this "perfectly designed? What portion of these underwater shapes do you think are efficient? There's nothing efficient about it, it's an80 year old design and it drives like one, but if you'd any real design or antique yacht experience you'd know this. Yea, it's a classic all right and a set of hull shapes everyone abandoned 50 years ago! Let me guess you don't know why, right Michael?

[frank smith]

Gentile men , where should I look for a more modern hull form , keeping in mind reasonably low power high speed turbo diesel . I think modern materials should make
it lighter than the Atkin's model. I can see how it can be light and fast , but I would not want to loose the wholesomeness of the type , I am thinking a pick nick type hull with out the lobster boat look.

[michael pierzga]

Well Frank, Im not familiar with modern North American low power motor boat designers.

In Europe the Italians and Dutch covet them.

The designer Nigel Irens is the master at low power motor boats . He holds the records for distance covered ,at sea , per liter of diesel. Very attractive boats suitable for diesel electric powerplants. Have a look

http://www.nigelirens.com/ldl/index.php

I cant remember the Italian designers name. He is based out of Venice. Try googling

[PAR]

So, you can't answer the questions posed above, can you Michael. Why is that Atkins design efficient? What makes it perfect? How does it act in a rough slosh? Back up your claims of the perfect design Michael, particularly in light of the 3/4's of a century of powerboat design evolution since it was drawn. Interestingly enough you mention Nigel Irens designs, but he has enough sense to not use these 80 year old concepts, not a hook among any of his designs, nor concave sections either. Why is this Michael?

[michael pierzga]

Sorry Frank, I couldn't remember the Italian designer...But I did remember a very talented American you might want to study.... Chuck Paine . He designs to traditional values. His Magellan Gulf Stream patrol vessel is a beautiful efficient craft. Perhaps study his thoughts.


" her bottom is a sophisticated ,steeply veed WARPED BOTTOM, with round chines forward
and lifting strakes for comfort in rough waters, aggressive spray chines to keep most of the spray from the
windshields, and sufficient power to carry on into Gulf Stream seas at up to forty miles per hour. "

http://www.chuckpaine.com/pdf/74magellan74.pdf