Mating Light Weight Traditional Hulls With Modern Stern Drives And Outboards And Electronics?
Bob at the helm. Go Bob Go!
Fellow Woody Boater Bob Rosenquist recently enjoyed our little Condenser issue debate and of course that ignited a fun story and possible larger debate for all of us to have more uneducated opinions about. There never is a wrong answer here. Oh for sure your an idiot, just ask your wife! Anywhoooo, here is Bobs submission to the panel of experts. My god have mercy on you Bob…
Bob and boats go way back! Here is Bob’s mom and dads boat
Over 30 years ago I started sailing and continued until a couple of years ago. Life changed as it always does and my sails wore out at about the same time. I will always love the feel of sails filling with wind and the sensation of a sailboat deck coming to life. The decision was made to sell the sail boat and move on; but this was not a sad end, just a chance for a new beginning. After many months of research and several disappointing trips to look at old fiberglass motor boats we decided to visit a wood lapstrake boat. It was the first boat my wife and I looked at that looked better in person than in the pictures.
This was a bit ironic because my first sailboat many years ago was a wood sailboat. Now I’m reading Woody Boater while waiting for our semi classic 1987, 24 foot hardtop Skiff Craft to receive some attention to make sure it is ready for the next thirty years of cruising the Great Lakes and the mighty Mississippi.
A recent story about points verses electronic ignition prompted me to email Matt and asked him if he would be interested in a story examining the possibility of highly efficient wood boating in the future. I have been impressed with the large and knowledgeable on-line following that Woody Boater established and I hope to start a conversation so that I can learn more.
The engines aft. Outdrive Goodness?
As you can see we have an IO. Matt kindly pointed out, “Outdrives are a no no in this part of the boating world. A dead end for resale. These boats are all about history and the look, not necessarily speed or efficiency. But it’s an interesting question, and sooner or later we need to embrace stern drives, because they are part of the next wave of classic boats.”
I found this interesting article by Eric Colby in Boating magazine comparing the efficiency of inboards to IO’s on the same hull. This led to more questions considering trim, weight, and horsepower requirements in wood boats. HERE
“We had to settle it right from the start. Everyone wanted to know if stern drives are faster. And, for once, the boatyard rumors were right – stern drives fly. The 260-hp stern drive boat ran 47.1 mph at 4600 rpm, while the 260-hp V-drive hit only 34.5 mph. No one expected that much of a difference. The 300-hp V-drive did a little better at 38.2 mph.”
First question to the Lyman and Sea Skiff owners: Could a Lyman 25 sleeper or similar size boat add over 12.5 miles to the top end using a stern drive? The article attributes most of the speed advantage to drag and the angle of thrust. However the Lyman and Chris Craft have another advantage, natural buoyancy. The specific gravity of Douglas fir plywood is approximately .56 verses fiberglass in a range from 1.3 to 2.0. The majority of the buoyant force would be located from the beam to the stern on plane.
Second question for Woody Boater readers: Is this buoyant force one of the reasons the Lyman, Sea Skiff, Skiff Craft and other wood boats come out of the water flatter with very little trim?
Back to the article, “Of more real-world importance on a boat like the 290 Amberjack is fuel consumption. At wide open throttle it was about the same for all three boats. But when comparing fuel consumption at the same speeds, the stern drives again had a decided advantage. The stern drive ran 34.7 mph at 3500 rpm, pretty much the same as the 260-hp V-drive's 34.5-mph top speed. In terms of fuel consumption, the stern drives burned only 22.8 gph at 3500 rpm versus the V-drive's 40 gph at WOT. At 4000 rpm the stern drive boat hit 39.4 mph and consumed 25.2 gph-about 1 mph faster than the 300-hp V-drive's top end, which ate 40.6 gph at the same rpm. Those numbers equal big advantages in speed and economy.”
The outdrive at work
Third question: Could the lighter weight wood boat have an even larger performance gain then the fiberglass hull that was tested? It is very hard to beat the wood strength to weight ratio. It was one of the reasons that boat builders like Lyman and Thompson were slow to embrace fiberglass in the late 1950’s. In boating magazines from the time period the discussions were centered on the new lightweight building materials like 5200 sealant and Chris Craft grade marine plywood that could create a strong, light weight, splash and go clinker-built boat.
Two loves!
When we dropped our boat off at the Skiff Craft factory last week my wife and I had an on-line conversation with a Skiff Craft owner on the owners association web site who said that I should be able to cruise at 20 to 25 mph at two to three gph with the little V6 mercruiser in the boat. I won’t be able to test this claim until next year so I would like to hear from other Woody Boaters about their real world fuel consumption experience. It would be great to hear from Boaters Dick and Janet Baner that are working on the Great Loop in a 24 foot Skiff Craft.
It intrigues me that classic wood boats could be a small part of the future of affordable boating. There is an aspect of back to the future using time-tested soft-riding wood hulls and high tech engines. There is also the added benefit of the renewable nature of wood verse fiberglass. I hope to hear from knowledgeable folks with insight on the questions posed in this article.
Lots going on here. The stern drive is much faster and more fuel efficient because it has less drag and because it moves the center of gravity aft and allows the boat to plane with less wetted hull area, especially with adjustable trim angle.
The boancy from wood is nonsense. The weight of the boat and the location of the weight matters, not the density of the material itself. Boancy comes from water displacement at slow speed and a lifting force on plane. When talking about planing speed, the hull design will have a huge impact. The depth of the V at the stern, the extra surface area from lapstrake S or spray rails or other features. Modern fiberglass boats designed for an out drive will likely benefit from it much more than an old wood hull.
For the second question, the forward CG and physics of an inboard that hurt too end speed are why they get on plane so well. That is why ski boats still use inboards.
Third question. Not likely. The complex shapes that give modern hulls their performance advantages would be difficult to reproduce out of wood. Light weight composites would do a better job of creating a low weight high performance hull.
M Fine
My old Skiff Craft and my Dad’s Cruiser Inc, both come out of the water very flat. What do you think contributes to that since both have the weight of the moters in the stern?
We owned a wooden stern drive powered boat for 12 years. She was built by the renowned Arno Day in 1970 as a stern drive. When I first looked at the boat I had my doubts, but I came to appreciate the good points the 160 HP Mercruiser provided. Here is what I liked: no engine box in the middle of the cockpit, quiet, smooth, able to steer in reverse, economical. We cruised at 10 kt @ 2700 rpm and at 3700 could hit 15 kt.
Another shot of One Fine Day
One more
I think I/Os are already a big part of modern wood boat building. The early Sterndrives had some troubles and got a bad rap because of it. Today they are reliable and efficient.
There were a couple of wood stern driven boats on the St. Johns River Southbound cruise this year. One was a Skiff Craft (that I think was there in 2014 also) and Doll Baby (shown here).
This is a better shot of this beautiful boat.
Here in Maine we even have a wood boat running surface drives. WB did a story on her in 2009.
https://www.woodyboater.com/blog/2009/01/06/hodgdon-yachts-and-rooster-dgdang/
Combining old and new technologies is beneficial but one must absolutely positively only use original zippers.
The sterndrive has been around commercially since 1959 and I don’t believe they are a “no-no” by any means. In fact, Greavette Boats incorporated sterndrives on wooden boats since 1960. Personally, I wouldn’t want any other drive type.
Even today there is still quite a performance difference between sterndrive models. Volvo being well built and “bulletproof” units while Mercruiser is lower drag with higher performance and better fuel mileage.
M-fine is correct when he talks about hull shape/design insomuch that the wetted surface is paramount to top speed. However, concerning recreational boats, I disagree with the idea that these shapes are difficult to make out of wood. This only applies to race type hulls with stepped hulls and other performance features rocker/hook. Again, in recreational boats, plywood is the light material of choice for performance and can be quite a bit lighter than a commercially available fiberglass boat of similar design. But, I digress, this is not about wood v. fiberglass.
Further, I would postulate that hull design, specifically a small deadrise, is why inboards plane so quickly and an I/O of similar design will do the same or better (Ski boats CG are predominantly designed for handling while towing a load).
My case and point is illustrated by my wooden 18′ Greavette I/O that has a 20* deadrise (deep- V). It is lighter than an 18′ Donzi Classic 2+3. It is one of the quickest planing boats I have ever seen. However, due to lack of lifting strakes and larger wetted hull surface it cannot achieve the same top speed as the 24* deadrise Donzi.
At the end of the day sterndrives are more efficient, better performing, easier to handle, give better fuel mileage and have been used on wooden boats (as factory installed) since their introduction to the market.
Here’s a 1961 Greavette Sunflash with an Eaton sterndrive
Chris Craft in the 1980’s took all of this a step further with their fiberglass scorpion line of boats. They created the Ski Jack which used an inboard engine that was attached to a long drive shaft that was then connected to an IO outdrive. It was the best of both world of engine placement and IO outdrive control. The driver/rear facing seat is the engine box.
well, here is a cool and informative thread, for sure! Like Matt, and us both being from VA….around here stern drives are a no no….but maybe the engineering has caught up with the technology. Keep this debate going…..interesting!
John in Va. (going boating TODAY!!!)
additional thoughts: I have often wondered whether old twin engine cruisers, reduced to trawler speeds by age, safety concerns and fuel cost, could not benefit and extend their usable life…but going to single engine stern drives? Conversion would be easy…..space, plenty, cost better than dual replacements.
Could a stern drive hooked to a low HP high torque diesel be connected to a stern drive unit and work properly…if slowly?
You would gain steerage in reverse/docking etc. I would like to try doing this some day.
John in Va.
Diesel marine engines by companies like Yanmar, Volvo, Mercury, FNM, Hyundai, Steyk, Iveco and Lombardini (to name a few) already exist for packaging with mercury or Volvo sterndrives.
A great solution
John: I actually saw an old cruiser about two years ago that had been converted to twin I/O’s. I wish I had gotten more information about it. Was a really cool boat out of Boston.
Sean is right, sterndrives are more efficient, better performing, easier to handle, give better fuel mileage and can be easier to trailer than an inboard. I’ve restored an 18′ Lyman I/O and it came out beautiful and was a joy to run. The problem is they generally don’t command the resale value as the inboards and I think the issue is people are scared of being able to troubleshoot and source parts for vintage outdrives that are over 50 years old. There are far less moving parts and things to break on an inboard compared to an I/O which is the biggest reason I tend to stay away.
I’ve also found that the vintage I/O on a wood transom trap moisture and can lead to rot over time if not installed and bedded properly. I/O’s also do not run as level since the weight isn’t centered and they tend to pound more on Lake Erie. I grew up on a 24′ Skiff Craft and have since owned only Lymans, 23′, 26′ and 30′. The quality in ride isn’t even close and the sound of an inboard is one of the best parts!
Pounding has more to do with hull design rather than drive design. Deep V or, large deadrise boats are designed to handle the rough stuff. Just look at any of the offshore performance boats (99% sterndrives). 24 degrees seems to be the magic deadrise number for offshore.
I have not had your experience with transom rot on an I/O woody… of course the through hull transom cut must be sealed form the start… that’s a manufacturing issue.
As for reliability, the old Eaton had some issues as did OMC. If you stick to Volvo or Mercruiser reliability, parts, servicing information are all easily attainable.
Sound is an issue of either through prop or, through hull design… Ask the Donzi guys about sound! I think the wooden hull resonates any motor used.
I HAD A 4.3V6 I/O IT BURNED 7-8GPH AT 3500RPM
ALSO YOU COULD COMPARE I/O TO OUTBOARDS
2 STROKE VS 4 STROKE
Check this out for fuel mileage:
http://www.boat-fuel-economy.com/mercury-mercruiser-4.3-262-fuel-consumption-us-gallons
Why do many I/Os or stern drives tend to walk the transom back and forth at low speeds. One of our friends have a Chris Craft XK19, and they can not run the boat straight without constant steering compensation at idle. I have heard the same complaint from other stern drive owners.
It’s an acquired skill. Make small corrections and you’ll get the hang of it.
The deeper the prop is in the water for an i/o the less it will walk left and right.
IMHO
The extended transom with an OB is worth considering
When I bought my U-22, the seller (who owned a marina), said that he did not get rich by selling boats, but by fixing and maintaining outdrives.
My view is that the CG gives me the ability to adjust the speed for ANY sea condition and still see ahead and be efficient compared to the “all or nothing” bow rise of a stern drive getting on plane. Granted, hull shape does come into play here as well.
I have a 350ci engine and I get between 2.5 and 3.5 MPG depending on speed; 3000 rpms is more efficient than 2,000 rpms.
Having said that, I want my next boat to be IO for the sake of maneuverability, MPG, and to raise the outdrive when needed. Oh, and get a bigger cockpit!!
Kevin F
As mentioned we are using our 1983 24 ft Skiffcraft hardtop to do the Great Loop a section at a time. So far have completed over 2000 of the total 6,000 miles. I started out with a 22 ft Sea Skiff Ranger model, then switched to a Carver 19 ft outdrive with a 4 cyl mercruiser 110 hp, and now the Skiffcraft with a 4 cyl mercruiser of 188 hp. While the exhaust sounds of the Chris are magnificent, the fixed underwater gear are sometimes problems in cruising. Outdrives are a lot better in many ways, not the least of which is steering in reverse. We do our loop sections running with another SkiffCraft, a 1984 hardtop running a v8 and operated by John and Carolyn Thompson. We are all lapstrake (Clinker) fans.
Dick Banner could you tell me if you had a great deal of prop walk at slow speed and what was your most economical cruise?
We plan to go down the river from in sections in the next several years.
Nothing against IO’s, but I can’t make em look right stuck on the stern of a wooden boat. Not pleasing to my eye. I don’t think you’ll see any antique classics going for the IO upgrade any time soon.
I will keep my inboards. I/O’s still have reliability issues. I am always seeing guys fussing around getting them fixed/replaced. Many moving parts = problems. They may be good for ease of docking and such but at slow cruising speeds they wander like crazy. I vote no on I/O.
I would like to have seen a comparison with a straight drive (not a V-drive with the extra drag) vs a stern drive. Also, different props could have been employed. Doesn’t seem quite fair to me. It has always amazed me that people prefer a system that makes two right angle turns, keeps half the gearing under water and is complicated and expensive to work on. All that hardware just to put a prop in the water. Give me a straight drive flathead any day.
The Volvo IPS drive with counter rotating propellers may be the solution for those wishing efficiency but wish to retain the appearance of an inboard drive.
This is not a new problem. Herb Ditchburn invented a hydraulic stern drive which he patented in Canada in the early thirties. See picture attached. While its efficiency is
unknown, it does have the virtue of simplicity.
I would like to know what props the inboards where using. Where they the old style 3 blade? If so the new style ACME props would make a big difference in the performance.
I recently finished installing a 350 270 hp at the crank on the 283 Chris Craft flywheel forward setup in a 1939 21′ utility. With an ACME prop on it it tops out at 46.5 miles per hour. Comes out of the hole faster and is only half a mile an hour slower then the owners sons new 120,000.00 Ski Nautique.
Also sterns drives have several different gear ratios to choose from to work best on a given hull design and also to run bigger props.
The comparison test that was done is not a true apples to apples test.
A big thank you Matt for running the story and to all the different insight!!!!!
The wandering experienced by the boats at low speed mentioned above is more a function of the deep-v hull than the drive system. I’ve been driving boats all my life and can’t keep a deep-V in a straight line while idling along. As for outdrives, yes, they help make boats easy to handle, but are expensive to maintain and require significant maintenance to be reliable, particularly if used in salt water. Give me a straight drive or outboard any day! I won’t own an I/O.
Dick Banner could you tell me if you had a great deal of prop walk at slow speed and what was your most economical cruise?
We plan to go down the river from in sections in the next several years.
M Fine
My old Skiff Craft and my Dad’s Cruiser Inc, both come out of the water very flat. What do you think contributes to that since both have the weight of the moters in the stern?