Jump to content

Ken_Potts

Slow power boat

Recommended Posts

Lately I've been thinking about actually owning a stinkpot.  There's lots of good boats out there that can go fast but I've had some difficulty finding efficient slow boats.  I'm hoping to power it with something like a 20hp diesel and I'd love to be able to cruise at 8 knots but I don't actually need to go quite that fast.  It's important that we have a nice open aft deck with shade because it gets quite hot here, so whatever I build will have a roof over the aft deck, even if it's a fabric one.  Spartan overnight accommodations would be nice but aren't completely necessary.

I finally came to the conclusion that I'll have to go with an old design if I want a nice, efficient, low-power slow boat.  My current favorite is William Hand's Zenith http://www.dngoodchild.com/5468.htm although I do like Bolger's Fantail Launch, too.

A note about local waters:  In addition to the nice, calm and flat ten miles or so of Swan River here, we're interested in taking weekend trips to an island about 10 miles offshore or other destinations down the coast.  Although we'll pick our weather (we've got the sailboat for windy days), it's pretty normal to have winds of 20 knots+ in the the afternoon.

One more qualification:  My wife is not interested in owning a boat that is unattractive (I love her sooo much).

Anybody got ideas?  Don't be shy, I like looking at boat pictures ;)

 

To recap:

- 20ish HP inboard

- Large, clear aft deck with roof/awning (wicker chairs and cocktails? small tugboat?)

- Efficient - Cruise at as close to 8 knots as practical, without working overtime to pay the fuel bills

- Head turner

Share this post


Link to post
Share on other sites

A 25' boat is a lot of boat, perticularly if power.

 

Posted Image

 

Posted Image

 

This is one of my designs. It's shown with an outboard, mostly because it's the logical route for most, but I have a few varations of this hull that will permit semi plane motoring. A 20 HP inboard will limt you to displacement speeds (8 - 9 MPH) as this is a big boat. Full standing headroom in the enclosed pilothouse, V berth forward, standup head, etc. She was designed for cold weather operation, so the pilothouse is longer then typical on a 25' boat, but it could be shortened without difficultly.

 

There are a lot of designs in this size, but not a lot of modern displacement speed versions. The aestedics can be changed to suit any "era" if a perticular style is desired, so focus on an efficent hull and also on a build method you can live with. For example, you can pick one of the old Billy Atkins harbor launch designs, which will be efficent, but it'll also be twice as heavy as necessary, if a modern build method was employed.Sso be careful what you wish for, as you'll have to pay for, cut and install all those extra pounds.

Share this post


Link to post
Share on other sites

Yes, the relationship between weight and cost is an issue - As is the cost of wood in WA. If I wanted to build Zenith to William Hand's scantlings I'd have to be a millionaire, so I won't be using that design unless I adapt the hull shape to modern methods and materials. That's why I'm looking to see if there are any more modern displacement designs.

Your Cooper Jr would certainly be a nice option. I'd be tempted to slice off the pilothouse just behind the windscreen to make a HUGE covered cockpit maybe with a table over the engine cover (if an inboard engine was installed). It might be a bit more roomy than Zenith. What's the beam at the waterline?

One of the reasons I'm looking at boats as big as 25' is to get the waterline length to get me close to 8 knots cruise speed. The reason I'm looking at such old designs is they were designed to make good use of low-power engines. I'd hesitate to put a heavy 20hp inboard into a boat that was designed for a modern 75-250hp outboard.

Share this post


Link to post
Share on other sites

Modern low power designs do exist. I have a 28' displacement powerboat, that is the big brother to Cooper Jr. It's capable of nearly 12 MPH (about 10 knots) and uses modest power. Of course, this is the best it can do, without an atomic reactor powering her.

 

There are displacement designs though these, in the size you're looking at, will at best see under 7 knots. The semi plane mode is a hard thing to hit. Below these speeds, you don't need much power, but to "climb the hump" you need much more HP or have to cheat with clever hydrodynamic tricks. In this vain you may want to look at some of the "Sea Bright" skiffs. Their unique boxed keel and hook can offer semi plane speeds, with modest power. The "Jersey Blue"  (Atkins) is a good example, where a 25 HP inboard might get you 10 to 12 knots with a 40 - 50 HP inboard jacking this to a max of 17 - 18 knots. There are other examples of this design treatment. Jesrey Blue is a carvel build and will need some upgrades to bring it into the 21st century, but not an unreasonable thing to consider.

Share this post


Link to post
Share on other sites

Thanks for the pointer to the Sea Bright Skiffs - Jersey Blue certainly fits my criteria.  I started poking around looking at other Atkins designs and found Sargeant Faunce - A design that seems to exceed my speed and power requirements handily, though the accommodations are a bit lacking for our requirements.

 

http://atkinboatplans.com/Utilities/SergeantFaunce.html

 

If the speed and power claims are true this boat is a good illustration of what can be done to defeat the dreaded hull-speed rule of thumb.

Unfortunately, it would be difficult to shade the cockpit of such a narrow boat and our temperatures get well into the hundreds pretty often here.  The classic Perth powerboat has a cabin forward to sleep in, a flybridge to help avoid reefs and a (big) aft deck that is sheltered from the sun by a roof and side curtains (google Randell for some local design examples).  There must be a boat out there that has just a little more beam to accommodate the roof/awning and some space to walk around the wicker chairs.  Maybe something halfway between Jersey Blue and Sergeant Faunce.  After all, both boats are capable of more than my target 8 knots max cruise speed and my favorite layout is large, clear decks (less furniture, less weight).

Share this post


Link to post
Share on other sites

 Sergeant Faunce is a 5:1 beam/length ratio boat, so it's very easy to propel, particularly with low power. With less than 5' of beam on a 25' boat, you'll find elbow room quite precious. This is the "rub" with lean designs. Bolger used this technique frequently, but most find it difficult to live with, which is why we see lots of fat boats with 300 HP hanging on their butts. 12 knots is possible with this boat, but you'll feel guilty about an 8' long cockpit and 16' of unusable deck space.

Posted Image

 

Have a look at Everhope, a 20' long, 6' beam Sea Bright that will do about 14 knots with your 20 HP inboard and can get slightly over 20 before she maxes out, because of hull shape restrictions. She has a lot more usable internal volume for her length.

Posted Image

 

 
 
Sergeant Faunce

Share this post


Link to post
Share on other sites

Everhope's a good name for a fishing boat.  The tunnel stern reminds me of a coble.  I went fishing on the North Sea once in a mini-coble that  the owner called a pebble :)  14 knots is way too fast, though - I think I like a stretched Everhope or a fattened Sergeant Faunce. ;)

Years ago I thought about putting together a powerboat to camp/cruise my way as close to Montana as I could get from North Carolina.  I was picturing the kind of boat you see on the Amazon and other huge river systems.  A little tiny motor and a 10:1 or 15:1 beam-to-length ratio.  The plan was to run down the ICW then across Florida and up the Mississippi and Missouri rivers.  If I had seen the Sergeant Faunce back then I might just have gone for it.

I'm in real trouble now - I just ran across an ad for a Volvo MD11C for $500 and it's just down the road.  No word on whether it runs, but it appears to be complete - Gearbox, starter, alternator...  Wish I knew more about diesels.

Share this post


Link to post
Share on other sites

Good morning, or evening to you sir. I got some jigs that's fitting for your requirements that can be paper patterned with some mods. Of course you can do the Bluejacket too, and I know Tom would just love than inboard being installed in his boat.

Share this post


Link to post
Share on other sites

The Volvo MD11C is a nice little 23 HP engine, but it has been out of production for over 3 decades. Parts are still available, but it's a pretty old school setup, which may or may not be appealing to you.

Share this post


Link to post
Share on other sites

Hey Paul,

I talked to a friend today.  He built an S&S 34 back in the 70's and still wins races with it pretty regularly these days despite being one of the heaviest in the local fleet.  I asked his opinion of the MD11C and he said I should absolutely NOT buy it.  He said it's a good engine and all, but he spends lots of time collecting parts in case he needs them and there are some parts (blocks and heads) that should be wearing out on the best-preserved engines any day now and they aren't made anymore.  I'm inclined to take his advice, mostly because I know he really likes the engine in his boat and it seems incongruous that he would advise me not to get one. The real kicker was that he knows the engine that I found for sale (it's a very small world here in WA) and he's still ofhte opinion that I shouldn't buy it for more than $50.

 

Capt Oyster,

Good to hear from you!  I hope you and your lovely bride are weathering the winter well.  You've got me almost talked into building a faster boat than I want.  I remember well your latest-generation show boat and all of its conveniences (and efficiency).  I may well take you up on your offer of paper tracings.

For some reason Tom's Bluejacket had slipped my mind.  I wasn't thinking of an outboard boat and I really don't want to exceed 8 knots but I've been watching videos of that boat remaining flat throughout it's speed range and I'm starting to rethink my engine choice - Athough I still really DO want a boat that goes "ta-pocka-ta-pocka-ta-pocka-ta" rather than "Brrrrrrrrrrrrr" :)  Maybe Tom will chime in here and tell me what he really thinks of me putting a big, heavy 20 hp diesel into his lightweight boat...

Share this post


Link to post
Share on other sites

Well  as we age, for some simplicity comes to mind. Add that to the fact that if you plan on gunkholing any, a straight inboard may give you some grief. Of course most displacement hulls do have some rocker in them and reduces some of the potential of wheel dings for shallow water use, but eliminates the ability to plane. But if you plan on trailering, WEIGHT should be the first criteria to consider, especially not knowing your regulations or restrictions for a tow vehicle. Launching ramps and the angles of them also comes to mind with inboard boats. some food for thought.. We also got out on the water last weekend and gunkholed ourselves, between all this crap of a marathon winter of cold, ice and snow. We had the water to ourselves and also did some geocashing on the barrier islands, a cool hobby for old folks too. So that's whats happening at the homefront.

Share this post


Link to post
Share on other sites

It's good to hear you're managing to get out despite the winter.  I still check the local (NC) news and it looks like it's been a pretty harsh one.  We've had some good heat here this summer but I'm not complaining.

We don't need to worry about draft as much here as in NC.  A 2 foot draft would allow us to go almost anywhere.  Also, we're not necessarily looking to have a boat that's easily trailered - This one will likely spend most of its life on a mooring or at a dock.

Share this post


Link to post
Share on other sites

Keep the ieas coming - They're good. I'll probably end up with an outbard eventually anyway (if it wasn't the better overall choice why would almost everybody have them?)

Share this post


Link to post
Share on other sites

Just a thought, how about the BandB  Yacht Design Outer Banks designs? You would have the added benefit of going faster than your 8-10 mph cruising speed if you need to to get in before a storm. I spent most of my cruising time in the 10 mph range with my OB 20 and was very satisfied with her performance.

 

http://bandbyachtdesigns.com/obx.htm

Share this post


Link to post
Share on other sites

Hi Chick,

I actually hadn't thought of the OB20 simply because it's a faster boat.  I was very impressed with your boat even before you took me for a ride at the B and B gathering - And I guess it speaks volumes that the designer bought it from you :)  How does the boat feel at 7-8 knots and what's the fuel burn at that speed?  Large areas of our cruising grounds have an 8 knot speed limit.

  Do you have an opinion about the OB24 in relation to the 20?

Share this post


Link to post
Share on other sites

I will add a comment that pertains to almost any low hp outboard planning hull. You always give up some ride in the open water, even though if you slow down, rarely do you have to deal with pounding and discomfort.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...



×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.