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Outboards vs Inboards - a discussion  

October 27, 2012. Recently your webmaster engaged Mark Steinhilber (Rascal), a marine architect and frequent contributor to our website technical discussions, in an email exchange that started from a comment posted on the Forum regarding the size of outboard motor and moved into the general subject of pros and cons of outboards vs inboards in our Dolphin 24s. That conversation is below with minor edits.

An invitation is extended to Dolphin owners, past and present, to add their 2 cents worth.

Sent: Thursday, October 25, 2012 9:46 AM
To: Steinhilber, Mark
Subject: OB motors

Hi Mark
We had the following comment posted on the Forum  http://www.dolphin24.org/forum/forum_posts.asp?TID=208&PID=711#711

"I believe the engine well was originally designed to handle a 9.9 2 stroke ob. Personally I prefer a smaller motor (lighter and more fuel efficient), besides she's a sailboat. How often is one going to use the motor? The answer to that question will help one decide what size motor to use. In my opinion, the smaller the better."

I have looked at my stuff and I can't find any new boat sales brochures/technical info that actually says the 'recommended' hp for a Dolphin 24.  As a practical matter, I think there is enough reader feedback that a long shaft 6 hp is a pretty good choice for today - of course that is a heavy/4 stroke that stays fixed in the well.

Looking back at this  from the mid sixties/seventies perspective, and given that the original standard design had an 8hp  inboard, what do you think would have been/should have been the recommended (transom well mounted) OB horsepower for the 2 stroke motors of the time?



From: Steinhilber, Mark
To: ron breault
Sent: Thu, Oct 25, 2012 5:01 pm
Subject: RE: OB motors

From a designer’s point of view, the auxiliary propulsion would be sized to provide a cruising yacht the ability to make coastal transits in light or no wind situations in about the same amount of time as with sails.  It is seen by a knowledgeable designer to be of little value to install more horsepower in an effort to push a displacement boat above hull speed.  This is very inefficient for fuel consumption , and becomes very evident as one tries to go fast with a displacement hull, the boat will create substantial wake where the bow and stern wave try to consume the boat.

In my experience the (original) Palmer PW 27 was plenty of horsepower for the Dolphin.  One could easily approach hull speed with the standard two blade propeller, and actually try to push above 5 or 5.5 knots.  Full throttle would bury the transom and engine exhaust with the stern wave and was only done when one was in a hurry.  Normally a more modest throttle setting was used on Rascal and very little fuel was thereby consumed.  We rarely filled the gas tank under the cockpit sole more than once a season, and this would take care of transits to and from nearby YC’s for races and even to Watch Hill for Off Soundings races.  The tank would get topped off if there was a weeklong cruise to Block Island, Newport, or Long Island.  While the 8 hp PW27 may have been slightly overpowered for the Dolphin, it was what was readily available, and may have been the best option available.  The 6 hp Palmer Huskie may have been it’s predecessor and probably worked well too, but may not have been available in the numbers or timeframe needed for the early Dolphins.

The inboard engine made the early Dolphins truly  a desirable cruiser racer like it’s bigger cousins, Finisterre, BI 40’s, and the Bermuda 40.   Reliable turn key power was pretty standard in 35 feet and up, but a dream in the early 60’s for anyone sailing boats less than 28 or 30 feet .  But the new fiberglass generation began the evolution of the industry to lighter weight and cost savings.  Although the slightly larger Tartan 27 came out soon after the Dolphin offering small improvements that could be put in three more feet, she too was blessed with inboard power and the two boats competed through the sixties to this day.  But it was with the advent of the Morgan 24 (25) in 1965,  a very similar keel centerboard boat that exhibited the evolution of the spade rudder and the move towards lighter weight (and purchase cost), that used an outboard  in a transom cutout.

The Morgan 24 was a direct competitor with the Dolphin for buyers, as well as on the race course.  Other Morgan 24s showed up with Vire inboards, competing directly with the O’Day and Lunn inboard powered Dolphins   Soon, other new lighter displacement racers like the Ranger 26 followed suit offering an outboard cutout in the transom.  The Johnson 6hp became the predominant motor seen on these new production sailboats in the late 1970’s.  I had a 1978 version of the Johnson 6 on my J24 that served me very reliably through the 1990’s and still ran strong when I sold her.  Most racers found that the lighter weight of the similar 4 hp Johnson was fine for the newer and lighter weight boats like the J24, J22, etc, and were easier to handle and provided almost the same speed.  But, added weight while cruising can affect this capability. 

Most racers, who realized the amount of drag that an outboard causes, remove an outboard from the transom or a well and stow the motor low and near the longitudinal center of gravity of the boat to reduce pitching energy wasted.   Speaking of pitching, Dolphin and Tartan 27 sailors took great amusement with the sound and noises coming from the outboards on the Morgan 24s and Ranger 26s in a seaway off Watch Hill, or outside The Great Salt Pond/Block Island at Off Soundings in the mid 70’s.  But weight when racing eventually changed attitudes and so did the J24 a few years later.  Also note that long shaft motors are normally recommended for sailboats because the application was for a 20+ foot boat in exposed waters where considerable pitching would lift the transom mounted motor,  instead of the dynamics that a 12 foot skiff might experience on a river or lake.

It is no surprise to me that Marionette uses a Johnson 4, or that those motors have proven to be long-lived, of adequate power, and portable due to its light weight.  When they first came along, the main benefit of the 4 stroke 9.9 motors was that they were some of the first (Honda)motors that could be equipped with an alternator that could be used to charge the boat’s house and starting batteries.  But, with the weight, they tended to remain in the well.  Nowadays, solar panels can keep up the batteries, especially with conscientious use and replacement of lights with LEDs that draw only a fraction of the current that incandescent bulbs draw.  This brings the discussion up this millenium.

Could an inboard be replaced with an battery-electric motor to get in and out of the harbor?  Yes!   Would it be sufficient on a long cruise with a lot of adverse current?  Perhaps, if charging could be supplemented with a small generator to charge batteries and solar panels.  Wisp has shown how even a trolling motor can work.

Was the outboard well originally sized for a 9.9?  I don’t think so - in the mid 1970’s even though Evinrude had a 9.9 with electric start that was showing up in the well of new Catalina 27s.  But maybe Yankee thought the same feature could help similarly equipped Yankee Dolphin sell.  The Catalina 27 was very much a bigger boat inside.  You’d have to ask Yankee that question about the well size.  I think the Dolphin well was probably sized for the very common 6Hp and later, people may have found some 9.9s would fit, possibly with some additional modifications.  Some 9.9’s aren’t much bigger than the venerable Johnson 6Hp two-stroke which was a little bigger and heavier than newer imported 6 Hp two strokes, but I think people just found ways to cram the bigger motor into the well that was there.

The early saildrives that came out in the late 70’s or 80’s lost the portability for repair offered by an outboard, yet didn’t gain longevity that inboards and especially diesels are known for.  They did save some weight, they stayed low, were key starting, and didn’t require a stuffing box or rudder aperture.  True inboards are still considered very nice to have, but outboards have really proven their longevity, versatility, and portability for repair or replacement.

What should I say about the McGregor 26 with a 25 hp outboard?  I have no desire to waterski behind a sailboat under power, nor do I want to contemplate the flexural stresses on that hull at speed in a seaway. They may be very much at home powering around Lake Powell Utah, but I wouldn’t want to take one offshore.  Again, just my $0.02!

Mark S.


From: ron breault
Sent: 10/26/2012 8:57 AM
To: Steinhilber, Mark
Subject: Re: OB motors

Hi Mark

Thanks for putting so much time into this. There  are a couple of more performance questions/factors

Marionette takes a 6 sec PHRF penalty as an outboard driven boat, presumably because the assumption is that the outboard prop will not be in the water while racing (and possibly (?) because an outboard has less system weight than an inboard. Also, I think I saw somewhere that a folding prop on an inboard draws a 3 sec penalty. Another performance factor, I think, are the efficiency issues of an outboard of a given hp vs an outboard of the same hp, and location of the weight. For example you can use a high efficiency prop on an outboard for powered performance and with the same motor have no prop while sailing, while an inboard might have a folding prop that improves sailing performance over conventional props but then you are stuck with poor performance when the motor is operating - either in forward, or especially in reverse

Net, net - besides the performance issues, the  other issues like, upfront investment and maintenance cost differences, appearance,  resale value, convenience, and safety, of key start inboards, while loaded with pros and cons, seem to make an inboard more desirable (in my own personal view) for a cruising sailor. But for a racer/cruiser, and a racer, it would seem that the OB makes a good case for its performance advantages..,. and its cost advantages



From: Steinhilber, Mark
To: ron breault
Sent: Fri Oct 26, 2012 4:26 pm
Subject: RE: OB motors

yes, the outboard is the motor of choice for racers less than 30 feet or so because the latest motors, 4-5 hp, are very light, zero drag, and can be stowed below in an optimum location same as fuel cans.  But cruisers prize turn key diesels for safety, convenience and longevity.

The folding prop has improved greatly, and now the best ones actually feather the blades 90 degrees fore and aft and are very low drag, and feathering types can be used in a rudder aperture like the Dolphin's or Tartan 27. Penalty or credit is only relative to what the base boat is, inboard or outboard.  Its been 6 seconds difference between the outboard and the inboard with two blade fixed prop since the 1970's.  For a while, we sailed with a 3 blade fixed (solid non folding) prop to get an additional 3 seconds per mile benefit.   I think the 3 blade prop probably slowed us more than 3 seconds per mile, so I think racers tend to find outboard boats win more.

I think an inboard with a feathering prop should be 6 seconds slower than an outboard and a two blade fixed is three more seconds slower, and a fixed three blade prop should be another 3 seconds slower.  It wasn't a problem when Class B-2 in Off Sounding racing was all Marscot and Lunn inboards, along with Tartan 27s, Tritons, Wanderers, and inboard powered Morgan 24s.  But outboard powered Ranger 26s, Thunderbirds, Catalina 27s, and Pearson 30s had fin keels and spade rudders and therefore went to the C-3 or C-4 racing classes back on the day.

Today, the feathering props are very good and back down much better than old folding props.  Today, I'd think 3 blade feathering!












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