Please Advice on Hull Selection

[Val]

Hello everyone,

Would you advice me which one of the following two hull forms is more efficient for electric drive please?

Assuming that the weight, length, beam of the finished boats are comparably the same. The main difference here is the draft, one is much deeper than the other. I will use a 24V or 36V motor with about 400 lbs of batteries.

http://www.dhkurylko-yachtdesign.com/build.htm

http://www.selway-fisher.com/Steamup20.htm#SAPPHIRE

Many thanks in advance for your help!

-Val-

[duluthboats]

If you put 400lbs of batteries in that Whitehall, add the motor and some gear, you’ll have to stay on the beach.

Gary

[Val]

Gary, if built as designed, this Whitehall can take an additional 800 lbs load for the maximum draft of 9". Although, I intend to stretch the hull about 2' more to increase the displacement and speed. :-)

-Val-

[duluthboats]

The batteries would be a good swap for the boiler on the Sapphire. With the Whitehall the max displacement is 1100lbs. The boat weights 300, + 400 for batteries, + 50lbs for light trolling motor, + 200lbs for minimum gear. If you're under 200lbs I guess it will work.

Gary

[duluthboats]

Sorry for the one liners but I’m at work. Welcome to the forum. If I had to choose between the two it would be Sapphire all the way.

Gary

[Val]

I actually enjoy the humor, Gary! I do make such light-hearted one liners all the time. (And got snapped at all the time too!) :-)

About the Sapphire, would the deep draft make it less efficient than the shallow draft of the Whitehall? I don't intend to run the boat more than 5 mph. Just around 4 mph is ok for my purpose.

My main consideration is the maximun cruising time I could obtain with either one of the two designs.

I prefer the Sapphire too, however, I worry that its deep draft, i.e. more water to displace, will exhaust the batteries too quickly.

-Val-

[duluthboats]

I can’t really tell you which is more efficient. The Whitehall will likely take less power to travel a given distance. But will also carry less of a load. The way I would look at it, is if they went the same distance the Whitehall would need fewer batteries. (less weight) Tell us more about what you want to do.

Gary

[Willallison]

Can't help myself any longer - time for me to but in on this one also
As Gary suggests - there is a lot more to choosing a particular hullform than its ultimate efficiency, however at the sort of speeds you're talking about - less than the displacement hullspeed - then longer and thinner is always better and a round bilge shape should offer lower wetted surface area - and therefore, less drag - than a hard chine shape.
This would tend to favour the Whitehall. But if it isn't capable of carrying the desired load, then it's all somewhat acedemic.
What you really need to do is to figure out roughly how much weight you need to carry, where the boat is to operate and what you want it to do. From there, you can make a much more satisfactory decision about which type of boat best suits your needs.
Alas, in my case, bigger always seems better - and way beyond my budget!!

[Val]

Gary and Will,

I plan to use the boat for fishing and overnight camping in some big lakes where the waves can get as high as 5 ...inches. :-) Of course, there is no current to worry about. Wind might be a small problem but can be ignored. My intended speed is about 4 mph, less than the displacement (mainly just to extend the travelling time.)

The average load would be about 1100 lbs. That includes all the batteries, motor, instruments, fishing gear, camping gear, food, water, me and my ...rib.

I like the Sapphire since it is easier to build and can handle the load without any modification. But I am not sure if the deep draft would put too much a drain on the batteries.

For the Whitehall, it looks like less power is required to push it the same distance, at the same speed, as compared to the Sapphire. But to handle the load, I must extend the body length to about 2 more feet.

Whichever one you recommend, I will build it using a different construction method rather than the one given on the plan. The end result is that both boats would have about the same weight. (As they are now, the Sapphire is much heavier because of the extensive framing.)

So, to make it ...shorter, I want the most economical boat that can carry 1100 lbs, in calm condition, at an average speed of 4 mph.

It took me quite a few months to find these two plans. Also, for the amount of money I plan to invest in the batteries and the electric drive, I don't want to make a mistake in choosing the wrong hull.

I do appreciate your helping me to select the most appropriate boat for my purpose.

Also, sorry for not replying to you earlier. I got stuck in some major problems at work today. :-)

-Val-

[terhohalme]

Here is more or less hydrodynamically optimum electric boat for sheltered waters @ 4 mhp and weigh of 1300 lbs (bare boat approx 200 lbs). Narrowness is achieved by installing the batteries on the keel.

As you can see, there is nothing classic, just your demands and easy building from plywood by stitch & glue method.

Sorry about the dimensions they are metric, just cant handle your feet and toes ...

Terho

[duluthboats]

It’s a rainy day so I can’t mow the lawn. I finished most of the honey do list, well some of it anyway. Then I started to think about the Whitehall. I got out John Gardner’s, Building Classic Small Boats, and reread the section on Whitehall’s. They started as harbor work boats and had a reputation as a fast and safe row boat that could also sailed reasonably well. As the type became popular and more refined the topic of who’s boat is faster came up. Racing Whitehall type row boats was a big thing in the New York and Boston areas, 1860-1895. 17-20 feet, 5.5meters was the most common length. The Whitehall will easily achieve 4mph, 3.5 knots, with a good set of oars.

Now if you increase the Whitehall you have selected to 20’ the displacement should go up to just less than 1300 lbs. (guesstimate) So yes, your batteries will go farther in the Whitehall.

Now for a rainy day rant.

“I intend to stretch the hull about 2' more to increase the displacement and speed.”

“I will build it using a different construction method rather than the one given on the plan.”

Back in the days before I became an internationally read amateur small boat noodler, I use to fall in love with boat designs, but they usually needed just some minor adjustment to be perfect. Which I was happy to make the adjustment. Actually I still do it, but I don’t tell anyone. Anyway, most designs you find have been worked out very carefully and won’t benefit from changes in materials or dimensions. I doubt if you could improve Sapphire by changing its construction. Pound for pound, wood is one of the strongest boat building materials there is. And it’s easy to work.

End rant. Please don’t take this as criticism, just advice from someone who has a passion for small wooden boats.

Terho

Is this a stock plan of yours or did you draw this just for this thread? I like it. With a little bright trim it will be fine launch and very simple.

Gary

[terhohalme]

Gary

It is a simple proposal for this case. I just put the numbers to Michlet godzilla (http://www.cyberiad.net/michlet.htm) and let the software find her optimum shape and Cp. Then I made some basic calculations, modelled the hull in Rhino and checked her hydrostatics with Phaser. Took about a half an hour. But as I said no styling, only maths...

A rowing launch should be designed about one third the displacement and have slightly more form stability (wider waterline) and directional stability.

Terho

[fredrosse]

I have been looking for a steamboat hull, about 16 to 18 ft, and the cheapest way to go is a used fiberglas sailboat with bad sails and rigging. These hulls are well streamlined displacement hulls, suitable for your intended service.


This type of boat is available on ebay for around $500 with a good trailer. Some fiberglas work to seal the centerboard well, and install a shaft for propeller drive is required, much less effort than building a boat.

Having said that, I will be building my own hull, plywood flat bottom, the sailboat hulls are all too beamy for a sidewheel steamer.

[SeaDrive]

You should be familiar with Phi Bolger's Lily design. See the boat in the foreground here: http://www.geocities.com/pvanderwaart/PA020025.JPG

The hull form is a fairly elegant sharpie launch, not an elegant round-bottom model such as you contemplate, but the size and use are similar to what you want. Bolger published an detailed explanation of the electrical system, includes the whys and wherefores of the choice of battery, and the required diodes and charging units, etc. Several of these boats have been built.

[artemis]

Originally Posted by fredrosse

... Having said that, I will be building my own hull, plywood flat bottom, the sailboat hulls are all too beamy for a sidewheel steamer.

I would suggest, for a easy to build plywood hull for a sidewheeler, that you look at the boat plans at Reliable Steam Engine Co. http://www.reliablesteam.com . Rebel is 20' 4" LOA, 17' 1" LWL, 5' Beam, 7' Beam over paddles, and 14" Draft. It is a plywood hull and the plans are very complete including instructions for constructing the paddles. Reliable also has, on their "ENGINES" page, a "walking beam" engine suitable for use with Rebel. Check it out.

Ron Fossum