Smaller Sea sleds

I am starting this thread to try to gather information specifically about smaller, outboard powered sleds. Not so interested in bigger inboard powered boats. I have drawn up the lines for a 10 ft hull that is essentially a shorter, wider take on the 13ft Hickman of which at least a thousand were built by the Knapps in the 1920's. These were all powered by the outboards of the day. Not very big ones at that and there are stories of these things doing 30mph which was pretty good for the day and in fact pretty good for today when you compare them to RIBs of that size with much more hp. I would be happy with 20mph or less with a 6hp motor. My biggest concern is the prop running in aerated water, maybe you don't need to get very deep to get under the bubbles escaping under the transom.

 

How bout it Steve!

Brand new here, first comment. Forgive any rookie mistakes. I'm curious to learn about different designs and would like to offer what I know of, southern boats........I gues the first thing I would ask is, what is Hickman or Knapps? What are you trying to accomplish with the boat? Anyway, any advice on Trailerable Pontoon House Boat Design?

In addition, I've spent 25 years in the composite industry designing, building, installing custom systems for nationally known science and industry.

 

Steve, Tales of the Hickman sled running 30MPH, with an outboard, in the 1920s, is probably unreliable information. That is one of those tales that I, myself, sometimes tell: "the older I get the faster I was" or "the bigger fish I caught".

The Hickman was agreeably an advanced concept in its day. If you want to go fast with a 10 foot boat you do not need a complex design like the Hickman. A simple shallow vee hull with an 8 to 10 hp modern outboard will do 30 or better.

 

From your other thread:
"I'm planning on a 10ft length, which is typical for a RIB style tender for a bigger boat, an outboard is about the only propulsion that makes sense on this size boat."
Well then you have to make an outboard work.
You may be able to get away with a manual jack-plate but it's still going to ad weight and cost.
Unless you make your own out of 2x4's.

 

Albert Hickman invented and patented the inverted vee hull form in 1914, the Knapps built thousands of them in the 1920s. There are quite a few designs out there for trailable houseboat designs, i don't have much knowledge of the type. You could do a search for any existing threads or start a new thread specific to the type.

 

MB,
This is why i started this thread. Most of us that have an interest in sea sleds are aware of the claims but only very few have actual experience with the type to be able to confirm or deny those claims. So, my hope is that someone may be able to add something other than speculation one way or another. Re, the 30mph claim, using the Crouch formula it would take about 20hp to get that assuming 1000lb disp. Quite doable. I have watched quite a few you tube videos of modern rib tenders, one in particular, Sailing Parlay Revival did a specific video testing out their new 3.8m Highfield RIB with a 25hp 2 stroke Yamaha enduro motor and with only 2 people onboard, so, nowhere near 1000lb displacement and they showed the speed on a phone app and it topped out at 20.8 something, i don't know if it was mph or knots. We have a lot of 12ft tinnies around here and most of them are flat bottomed and pound badly at speed, Grummans are a nice shallow vee so should ride better but they are not getting anywhere near 30mph at 1000lb disp with 10hp, maybe running light, i don't know. I almost bought a 12ft Grumman with the intent of shortening it with a Garvey type bow but none of those small fishing boats have enough freeboard to carry a load safely.
My point is, when you undertake a design you start with a statement of requirements (SOR), as i'm finding out, a tender is a very difficult proposition. For a cruising boat the tender needs to be a jack of all trades, it needs to be able to carry the crew ashore, so good load carrying ability and good stability when boarding from the side, do expeditions well away from the mothership so reasonable speed matters (not 30 but maybe 15 - 20mph) It needs to be able to plane at 800 - 1000lbs displacement, a lot of tenders will only plane with 1 or 2 people on board. I could go on and on but suffice to say when i look at my complete SOR no hull shape checks as many boxes as the inverted vee, assuming of course that they can live up to the claims.

 

BB,
While the concept of running an outboard in disturbed water doesn't seem like it would work well to me, based on the fact that Knapps built so many of the 13ft models, all outboard powered it must. I think that maybe using a 20" long shaft on a 15" transom may be enough to get it deep enough to be in clear enough water. That looks to be about how deep the photo of the boat on the ways on the spooner central site is. It's not ridiculously deep but deeper than on a typical positive 10 - 15 degree deadrise boat would have. I really don't think a jack plate is needed and certainly not desirable since with frequent beaching i would not be wanting to go through 2 steps of raising the jack plate and tilting the motor when comming ashore. Every photo i have seen of one of the Knapps boats the motor is just mounted as on any boat.

 

You know best Steve. Good luck.

 

@Steve W , Crouch's number for the sea sled is the original set: hull and surface drive. My own sled with an outboard set extra deep does reasonably well, but not in the stratospheric range that Crouch's number would suggest.

The surface drive that Hickman invented was also revolutionary.

 

I have seen some photos of a very large Hickman sled on the ways with a surface drive and it was a very simple thing with the shaft coming through a gland in the transom with a huge prop, not at all trimmable or able to steer. the photo was to show the trim tabs which he used to steer which apparently did not work very well. So the prop was only biting into very disturbed water which i would not think would be effective at all but there you are. Since i am only planning a very small sled at 10 -11 ft and frequent beaching its a bit of a moot point as i will certainly not be trying to reinvent the wheel with the complexities of an inboard and surface drive so an outboard it will need to be. I'm thinking a 6hp Tohatsu 4 stroke at 58lbs or a Suzuki at 52lbs. There aren't many 8 horses these days as they were typically detuned 9.9s so they weighed the same and they are a big jump up in weight from a 6hp. One of my (many)reasons for exploring this hull form is the promise of speed with lower hp while carrying a load. To be clear i am not looking for silly speed, 15mph at 800 - 1000lbs disp would be plenty. Most ribs of this size can do that but need more hp so a heavier package hanging from the davits. I think you said that you have your motor set 5" deeper than recommended by the mfg and that looks to be something like what that 13ft sled has so that would be my starting point. Have you tried it deeper? Some other questions i have are regarding the load carrying claims, have you found it better than typical in this regard? How about the ride? I have seen claims of soft riding in rough conditions and the opposite.

 

Load carrying is absolutely massive. And the ride is great. The speed is about like a typical boat with the same power to weight ratio. To quote the late great Meatloaf, "Two outa three ain't bad."

 

Thanks DC, that is encouraging, what about maneuverability? when i look at the body plan drawing of a 13ft Hickman without the anti -trip chines it is not hard to see how it would dig in in tight turns while the drawings with the anti-trip chines look to me like it may slide out a bit, Still, that would be preferable to tripping i would think. Some of the attributes that appeal to me for my intended use as a tender is that it should be quite stable for boarding from the side due to the slab sides and max depth being out at the edges with nothing to detract from stability in the center, similarly, boarding from bow on to a dinghy dock should be easy and stable, good load carrying and good speed makes a nice package.

 

It steers so straight I can leave the wheel for minutes at a time. Going slow she'll turn ridiculously tight. And nothing seems to push her around. I have a 17' simple V hull commuter. When things are rough she needs constant steering. Serenity don't care. She's going where I pointed her.

 

Thats all good news to me. I'm less concerned about high speed or super tight turns, that's just party tricks. For my SOR, good load carrying, stable for boarding from the side or bow, low power requirement, ie, i would like a light 6hp rather than a 9.9hp to keep the overall weight down when hanging in davits or moving up the beach and it looks like this can be achieved. Thanks a lot for your input.