Ranger 24 Hull Dimples

[R Baker]

I guess the big question, is, do they work ? Do they reduce friction enough that reduced fuel consumption is noticeable ? If they reduce fuel consumption by, say 5% or even 10%, then what does that represent in dollars ? And, at what speed are the dimples most effective ? All of this came to mind after a visit and chat about dimples with an admirer at Bobcaygeon last week.

Now to continue on this esoteric subject.... The hull design of the Cutwaters has some features that I feel are superior to the Ranger hull design. It all comes back to friction... does the Cutwater 28 consume less fuel than the Ranger 29. A difficult comparison but of interest.

And, lastly....why is there no link to the Cutwater line on this forum ? After all there is considerable discussion from owners.

 

[SGIDAVE]

I guess the big question, is, do they work ?

Well...DIMPLES definitely work for golf balls and movie stars[emoji3]

Sorry couldn't resist

Dave

 

[Red Raven]

Interesting post...I wish I knew the answers to your questions. I doubt we will find the answers though. Here are my thoughts for what they are worth (exactly $0).

Dimples: may help a bit but probably mostly at higher (hydrodynamic) speeds that the R23 and C24 run. I suspect the impact is more in the 1% to 3% range and only at the top speeds. May actually increase drag at hull speed so like most of these things it depends on how fast you want to go. I wouldn't be surprised to see them added to newer Cutwater hulls but I doubt it on the tug hulls which are focused a bit more towards slower speed efficiencies and maximum volume/length.

Cutwater hull features: Yes, the Cutwater hull features may offer increased performance at higher speeds. These higher features require a bit more horsepower and thus the higher hp engines in the Cutwaters which adds cost. Note that when comparing a Cutwater to a Ranger Tug the closer comparison is to compare the smaller Ranger to the 1 ft larger Cutwater. The Cutwaters have a more gradual stem to handle higher speeds which makes the boat a bit longer for the same waterline length without much increase in volume. For example, a Cutwater 28 cannot be effectively compared to a Ranger R29 as the beam is significantly wider on an R29. The closest comparison would be the R27 in terms of overall volume in the boat. Even this would be difficult as the R27 is biased towards efficient slow cruising with still reasonable semi-displacement performance. Adding the Cutwater hull features to an R27 may improve the higher speed performance a bit but would potentially reduce the low speed performance, require more hp (if deeper V) and for some features (stem angle) change the look of the boat.

For the most, part such comparisons are fun to consider but ultimately as a consumer it boils down to what is available. If Ranger tugs (or some other builder) decides to add dimples and other higher speed/higher power features (read Cutwater) to a tug style hull (which they have now apparently done to some extent in the R23), only them does it really matter but it will still boil down to person preference for what you want to emphasize. We are really happy with the trade offs made in the R27 design but that doesn't mean that there couldn't be hull improvements for future buyers to consider.

 

[stwendl]

Perhaps this is not a satisfying answer, but there was a episode of the myth busters confirming that dimples in fact benefit fuel consumption and performance. I think the theory behind it is to break up the flow which works like glue.

 

[NorthernFocus]

We need an interested owner willing to experiment with their tug and report back results. I'll pitch in a ball peen hammer to support the effort :shock:

 

[tlkenyon]

It is kinda-sorta along the same lines as wet-sanding your sailboat hull to increase speed. The roughness of the wet-sanding traps the water near the hull and moves the boundary layer into the adjacent water so that the friction is water against water instead of water against the hull. Unfortunately, the wet-sanding also creates a very good place for critters to grow, hence its use on rather small racing boats like sunfish and hobies and the like.

The dimple idea kinda came from the golf folks. As the ball spins, the dimples cause differences in the speed of the air over the dimpled surface and Bernoulli creates lift, causing the ball to go further. Contrary to what the Mythbusters determined (don't get me started on their "Scientific Method") the dimples are not that effective for friction reduction on a non-rotating body. If they were, you would see them everywhere. There are also the considerations of the compressibility of the fluid (air vs water) and the speed regime (laminar vs non-laminar).

That being said, I will also donate a ball-peen hammer to the project.

 

[baz]

My understanding for why golf balls were changed from being smooth surfaced to being dimpled is that the air drag on a smooth surfaced ball is higher than one with dimples on its surface.

If the golf ball rotates as it flies thru the air with or without dimples will cause lift or negative lift depending on the balls rotation.

 

[tlkenyon]

Baz,

You are correct..and when the backspin is added to the equation, lift is generated and that adds to the distance.

When I took fluid mechanics in engineering school, my professor was an avid golfer and we actually did wind tunnel experiments on various objects and surfaces, including, of course, golf balls. He actually created an alternate geometry of dimples (trapezoidal) that actually made the ball fly further, but not legally if you are playing for money. We also did a bunch of hydrodynamic testing on surfaces to minimize drag. It was an interesting time.

Unfortunately for the real world, the tweaks do not have that much impact, and certainly not as much as marine growth, wind, waves, and all the real stuff in life. Kinda fun to think about, though.