Help With Economical Semi-Planing Designs

fcfc,

Thanks for the link to Chesapeake. I return the favour with another box keel boat, from S Oz.
http://www.duckflatwoodenboats.com/mainpages/mundoo.php#Published Articles

The solar powered Mundoo III is another in the line of lightweight cruisers that would do well on the River Thames. It's got me thinking!

Regards,

Pericles

 

Quality paint is my best friend. Varnished wood is used for accent trim only. Obviously cheaper and IMO much more appropriate for a "homemade" boat in today's "environmentally concerned" collective consciousness. As always, YMMV.

Best,

Leo

 

"My takeaways from these pages are:
Fine entry. Flat buttock lines. Light weight.
What other important ideas/features did your eyes pick out?
Best, Leo"

I used to live near the Antique Boat Museum in Clayton, NY. Old powerboats, some speed record holders of the day, are featured in their exhibits. The early engines (prior to surplus aircraft engines from WWI becoming available) simply did not have the power-to-weight ratio to make planing a possibility. Semi-planing was the best they could do. So I went there and sat or laid on the floor, studying the hull shapes, trying to determine what features helped them maximize their speed. I agree with your list.

I am guessing that a small B/L ratio is also assumed to be true. The fine entry pushes water aside gently. (Relative) Light weight minimized the displaced mass. Flat buttocks minimized stern squat. The small B/L ratio allowed adequate displacement with minimal frontal area. Additionally a long, slender hull allowed a gentle transition from water being pushed aside by the bow to water flowing under the low-deadrise stern.

I seemed to also notice one other feature- a gentle but noticeable rocker confined approximately to the middle third of the hull with a straight keel forward and a straight run aft. I can't be sure because these were old boats which might simply be sagging with age. But such a rocker would make sense. Without rocker that stern would likely be dragging in the water; not good at lower speeds. Also, at increased speed, power is applied low under the stern and increased drag would tend to concentrate at the bow wave. Under these conditions, would not the boat tend to squat slightly, rotating about that central rocker, presenting a more cutaway bow profile and a more flat planing surface aft? Perhaps this profile helped the hull to slightly exceed the confines of displacement hull theory and enter the indistinct semi-planing realm. This is only my guess; I'll leave it to the more experienced to decide if it may be valid.

 

I think probably. But do not expect the same finish, style and performance as the andreyale.

The other question is what else can you do with that budget and time ?
How does it compare to a homebuilt ?

http://www.yachtworld.com/core/list...h=30&toLength=36&currencyid=100&toPrice=45000

You have $15K left for maintenance. The speed will be lower. The fuel burn a bit higher. But there will be no comparison possible for resale value in future time.

 

Geez... How I hate it when someone rubs my face in reality.

 

Do this kind of light semi displacement boat exist for homebuilding ? I have found none. You can find plans for 65 ft sailboats, worth hundreds k$, but a moderate 30-33 ft powerboat : No.

 

Sadly but unfortunately, this thread has done very little to define what is a semi- hull, and what advantages or dissadvantages they have over a planning hull.
Wayne mentions the back 1/3 of the bottom of the hull as to rising, rather then the straight run aft of the planning hull, and the deeper forefootof the semi- hull.
But that seems to be about it as to hull shape. Leo posted pages with lobster boats that are semi hulls.Wonderfully performing boats.
And yes there are plans for semi hulls in all sizes reasonable available, if you know what you are looking for. One designer has been metioned in this thread with semi- hulls in the 30 to 33 ft. range.
Then again for a 33 fter plans, a wonderfull boat is the potluck by glen-l, a 33 ft. semi- hull. Lobster Boat. Excellent choice.

 

May be, but at 9250 lbs displacement and 100-120 hp, the potluck 33 will nearly cost twice to build and operate than a 5500 lbs 60 hp andreyale 33 clone.

 

I am looking at len 31-33 ft, displacement < 5500 lbs,preferably < 5000 lbs beam < 8'4" , power < 60 hp, inboard diesel. Top Speed > 14 kts.
If you know any design that match (homebuilt or production), please give indications.

And if you think there are unreasonable dimensions above, can you tell which one and why?

 

fcfc,

There are two Sam Devlin vessels that should suit your description, for which plans are available.

http://www.devlinboat.com/dctopknot.htm

http://www.devlinboat.com/dcbc29.htm

There are photographs at bottom of each page.

Pericles

 

The advantage of the semi plaining is that the hull forward stays in contact with the water.This is not great for high speed but fine for 14K.

By selecting a proper entry the vessel will be far kinder in rough going than the full plaining boats to the occupants.

Take a look at Atkins River Belle , and contemplate JUST the hull, place whatever deck and house on it as you require.

Building in Airex foam core is a very simple way to allow a complex hull shape to be built fast , strong and light.But unfortunatly not cheaply.

FF

 

Displacement 10800lbs >> 5500 lbs.
Beam 10'2" >> 8'4"
Power 250 hp >> 60 hp.

Do not fit.

Len 29'2" < 31"
Beam 10' > 8'4"
Power 130-200hp >> 60 hp.
Displacement 8400 lbs > 5500 lbs.

Do not fit.

I have looked for nearly 1 year. And I have found nothing even close.

 

FcFc- Neat, I see where you are coming from, the old time launch. I looked at the andreyale, nice looking and proportioned boat.
I take it you are wanting to push the boat to towing length, when you add in the length of the trailer tongue, and you are right at the width without a permit. Weight issue for a heavy truck or such.
There are a few boats that come to mind, one that looks almost the same is ruel parker 36 ft. commuter, but it is 3 ft. longer. Same weight and it uses a 90 horse outboard.
http://www.parker-marine.com/commuterpage.htm
The architect mmd, can be found on the wooden boat board, drew plans for the same boat but in aluminum, You could get him to draw a set in wood, at a reduced length of 33 ft. There are very good reports on the performance of the boat as well as stability and smooth ride.
Another design that comes to mind is the whio- it was featured on wooden boat a while back. It is 30 ft. long and only 7 & 1/2 ft/. wide, 3,000 lbs, and used a 60 horse inboard. This is a nice boat too.
And of course there are a couple boats by bolger, the idaho and tennessee I believe, They fit your weight, power and length roughly, and one is a lot longer as I remember. But they are flat bottomed plywood boats, that look kinda boxy and in my opinion are no where near or even close to being in the class of the andreyale, parker's commuter or the whio.
There are a couple of old time atkin designs in the high 20 ft. range that can easily be stretched 3 or 4 ft. by simple respacing frames. Atkin had a habit of using 12 frames on anything between 15 ft and 40 ft. by just increasing the spacing and size of framing and planking thickness.
Your 60 horse and 14 knots or 16 m.p.h. is pushing the engine to max, and the speed will be iffy, and not a cruising speed, you may want more like a 90 horse, so as to not push the power to the max. just what the parker commuter uses.
If you are serious, I would say to look at mmd's version and see about having a set of plans drawn to your specs, they will be well worth the price for the boat you want.

 

Here is the link to the mmd version of the commuter.
http://www.abco.ca/marine-abco36-pleasure.html
It is a little longer, lighter, and higher speeds.


Here is also a suggestion on a atkin boat, that could easily be stretched 3 ft. and could be converted to a outboard, particularly by using a bracket or manual jackplate and keeping the transom whole and solid.
I think it would make a wonderfull boat, and a little shorter for easier launching.
http://www.boat-links.com/Atkinco/Cruisers/Hope.html

--In reviewing the previous pages, I see where the 44 ftr commuter was listed and one of the bolger designs. too many pages to keep track of everything.

 

There have already been lengthy threads about the GRAAL.
http://www.boatdesign.net/forums/showthread.php?t=5073
http://www.boatdesign.net/forums/showthread.php?t=11670

I am not particulary found of outboards. And when you put a inboard in commuter 36, the layout become awkward.

The second issue is I doubt seriously about resale/real value of a custom designed custom built boat. Especially when the primary reason for custom design/building is that no other similar boat do exist. That simply means there is NO market.