Gimme Power !!

Most threads make at least one reference to it, so perhaps it is time once more to enter the fray with everyones (...well, mine anyway) pet subject - powering options:

Diesel Inboard
Diesel sterndrive with or without jackshaft
Petrol Inboard
Petrol Sterndrive with or without jackshaft
Outboard

Oh, and of course Trouty's Neutron Drive......

What's it to be ?

Me - I'm all outboard, for reasons stated previously. There is often concern about auxhillary systems on an outboard powered cruising boat. See http://www.sundownmarine.com.au/seaquest.htm
As an example, they use an immersion style water heater for their hot water supply. Even mid-range outboards pump out at least 40 amps for powering such things.....

This may seem like covering old ground, but maybe....just maybe, we might be able to get to the point of making a decision on this one via a poll some time soon......

 

Ah yes, how she’s powered will make a big difference in the design. I guess we should take care of that little sticking point. Working on my retirement boat has made me look at this from many angles. For a long time I was set on inboard power. I worked on the hull and interior. When I had everything the way I wanted it I started on details for the engine. Adding all that an inboard engine needs (ventilation, cooling water, combustion air, exhaust, prop shaft) always seemed to ruin my layout. I didn’t want to make the boat larger or make it difficult to maintain these systems. I ran out of compromises, so I switched to outboard power. My boat is not O-1 but close enough, so my reasoning would be the same. (flawed as it is ) Working this out on O-1 will help me also.

One big advantage is how easy it will be to re-power. A big disadvantage will be fuel, for some parts of the world.

The member count is now over 400. A 100 or so opinions on this subject would be nice.

Gary

 

Researching the choices

Before I make a decision I would like to know what is commonly used in a boats of this class and why. I would also want a cost of ownership comparison for the engine options.

To determine what boats of this class use, I went to the NMMA (National Marine Manufacturers Association) and looked at their statistical fact and figures. The estimates of outboard sales by year ( http://www.nmma.org/facts/boatingstats/2001/files/boatsales.asp ) shows that from 1997 to 2001 the sales of Express Cruisers that were equipped with outboards varied from 0.04% to 0.2%. The estimates sales of stern drive Express Cruisers ( http://www.nmma.org/facts/boatingstats/2001/files/hullmaterial.asp ) varied from 11.5% to 14.2% over the same period. From the Annual Retail Unit Sales Estimates ( http://www.nmma.org/facts/boatingstats/2001/files/unitsales.asp ) it appears that the remaining 85% to 88% must be inboards or Jet drive.

Another interesting reference is http://resolutionhost.com/BoatsAndPlaces/HowTo/BuyABoat.htm. Look at the section titled, "Power: Sterndrives, outboards. Inboards or jets; gas or diesel?"

Also, go to the buyers guide at http://resolutionhost.com/BoatsAndPlaces/BuyersGuide/_Main.htm and see how many "Express Cruisers" have outboards.

Cheers;
Mike Schooley

 

I'm not at all surprised that the bulk of so called express cruisers are fitted with either inboard or sterndrive engine(s). However, as always, the devil is in the detail - for instance, what % of those are trailerable? And how big is an express cruiser?

And you also have to remember that outboard design has come on in leaps and bounds in the last year or two, so it will be some time before the figures catch up with technology. In the first years when fibreglass was first introduced to the boating world, I imagine that a similar survey would have shown that >95% of cruisers were made of timber.....
As far as running costs go, I have some interesting figures regarding fuel consumption at home - I'll post them tomorrow.

 

Unless I decide to do a classic runabout, I will be using outboards on any boat I build.

A similar survey on aesthetics would show that at least 80% of the same Express Cruisers are butt ugly but that does not mean that we should follow their lead.

 

But Why?

Will;

The YachtWorld data shows the bulk of the Express Cruisers are in the 26' to 34' length range with three peaks occurring at 27'-28', 30' and 33'. Most on the Express Cruisers below 30' that I have looked at so far are trailerable. I have not found one over 30' that is trailerable.

I think the relevant question is why do "Express Cruisers" favor inboards and/or stern drives. I too like to plot my own course, but that doesn't mean I am going to leave the crowed channel and charge into the shoals just to be different. When I decide to depart from the proven path, I double and triple check my reasoning. So far we have determined that the beaten path for this class is not outboards! Again the relevant question is WHY!

You mentioned that Outboards have made recent improvements and this MAY explain it, but it could also be due to other reasons. There may also be a lag time for the consumer to learn that what he/she knew about boats last year is no longer true. Biases and prejudices take a long time to die.

One intrinsic problem with outboards is they tend to concentrate a lot of mass at the stern. This can be balanced by pushing more inert mass forward, but placing mass at extreme distances from the center of gravity increases the pitch moment of inertia by the square of the distance, this intern increases the tendency to porpoise in heavy seas and produce higher bending loads in the hull. This effect is compounded as the power levels increase (i.e. the GTi version will be worse). Designers have tried to counter this problem by submerging the outboard into hull in a well area, but this impacts the usable area and arrangement of the boat.

Tom;
Please humor those of us (or me if I am the only one) who do not yet know all there is to know about boats. I'm still learning, so I try to keep and open mind and I ask stupid questions.

Cheers;
Mike Schooley

 

Mike,

I suspect that you know as much or more than me about boats. I'm just an amateur that has been around long enough to develop prejudices. I do think that I can learn when proper force is applied though (a bigger hammer perhaps). I have built a number of small boats and spent a bit of study trying to learn about the factors that affect boat performance design.

 

Water Heatres

Will;

You mentioned running an electric water heater off the outboard motors 40 amp alternators.

Assuming you have twin outboards with 40 amp 12.5 volt alternators that would be 500 watts each or 1,000 watts. I looked up some outboard motors and found that their 40 amp alternators provide 40 amps @ > 3,000 rpm. Below 3,000 it falls off to nearly zero at idle speed (700 rpm). In addition alternator capacity is generally rated at cold operating conditions. Once the alternator heats up output is typically 10% to 20% lower.

I went to West Marine's pluming section http://www.westmarine.com/webapp/commerce/command/ExecMacro/site_search.d2w/report and found several water heater options. The "tankless" water heater looked like the lightest weight and most compact option so I looked at the smallest EEMAX Electric Instantaneous Water Heaters, the 20 amp model http://www.eemaxinc.com/marspec.htm. This unit runs on 120 VAC and requires 20 amps or 2.5 kW.

I looked at storage tank water heaters. The 6 Gallon Super Stor Stainless Water Heater http://www.htproducts.com/products/electric/literature/lp-02.pdf draws 19 amps at 120 VAC and the Raritan 1700 series 6 gallon requires 15 amps at 120 VDC. The Seaward Products Stainless Water Heaters 6 gallon model comes in either 30 amp or 50 amp versions. I could not find any electric water heaters that could be driven by stock outboard alternators. Maybe the alternators could be upgraded to higher output?

If not, to run these electric water heaters, without shore power, would require a generator or an inverter to convert 12 VDC to 120 VAC and a battery bank to meet the demand. The cost and weight of either option would need to be figured into the outboard versus inboard engine trade.

I searched for 12 VDC water heaters without success. I also searched for propane water heaters, but they all seam to have been removed from the marine market due to CO2 poisoning problems.

Cheers;
Mike Schooley

 

First thanks for digging up some numbers for us to look at. As the others have said though, the numbers only tell a small part of the story without the ‘why’. Seeing that we are straying from the pack, all we can do is to recheck our logic and make sure everything is sound. And maybe we should look at the numbers the other way – if there aren’t a lot of (or any) production express cruisers on the market doing exactly what we’re thinking of (outboards, etc.) that might mean there is the perfect market niche for this design.

 

At the same time, as you said, maybe the marketing of an outboard express cruiser also comes down to the long time it takes for preferences and prejudices to change and the kind of “collective” decision making which occurs as styles come and go. A few people get minivans – then everyone starts wanting a minivan. Next people start getting SUV’s, and now everyone has to have an SUV. Or around here dual wheel pickups have become the fad this year, but I’ve noticed that in almost every case the people who can afford the dualies don’t really have anything to haul, so the extra wheels are just for looks while the builders and masons hauling everything are driving the same 1980’s single wheeled pickups loaded down to their axles and getting stuck in the sand the same as always.

With my last boat I chose Stern Drives over Outboards because:
1.) I liked the "feeling" and sound of the engines over the higher pitch of the outboards.
2.) I preferred not seeing the outboards back there - I wanted a cleaner transom.
I think I mentioned that over the past few years I've used my boat for day tripping over to the other Islands just a few miles away mostly, and haven't made a chunk of time to take many longer trips. Now do the majority of boat buyers make their decision based on numbers and practical concerns, or with a large investment for a weekend toy, are the decisions based more on appearance, sound, and feeling driving them for a hour here and an hour there?

So then as the other thread discusses, we either have to decide on the "typical buyer" for this design (we know the capacity the design needs to have, but not the actual amount of use) before we can properly weight the factors, or alternately we can decide to design for the best overall design for an "ideal user" in this thread, and then let the design shape the market in the other thread. Will people buying a boat for this set of criteria really use the boat in this way? How many people with express cruisers use them enough to make fuel efficiency or higher maintenance costs even a fraction of the overall expense?

 

2 sites with LP marine water heaters.


http://www.astravan.com/specs.html

http://www.go-rv.com/online/1037/showproductdetails?catid=1077

 

Another 12 volt hot water supply - http://www.glind.com.au/default.htm

Everyone makes valid points - both for and against outboards - and all are worth considering, whether informed or not.

I think Jeff makes the most telling of points in the reasons why he has chosen sterndrives in the past - noise and appearance. The former can be addressed to some extent by clever design and insulation etc. And the 4 stroke o/b's are both quieter and "smoother" sounding than their 2-stroke counterparts. The latter is a matter of personal preference and is going to vary from person to person.
It is also true to say that the running costs for the average boater are far outweighed by the simple expense of owning the boat in the 1st place. Where things like fuel consumption become important, however are when you're trying to maximise range - or keeping weight to a minimum.

In a recent publication, I found these figures:

Volvo's tests reveal that a 5.7L sterndrive uses approx 80 L/hr at WOT and 35 at cruise - 3000rpm.
A mercruiser 4.3L v-6 consumes about 65L and 27L respectively.
The 3L Mercury Optimax o/b consumes 66L @ wot and 28 L/hr at cruise (4000rpm)
The 3.5L Honda 4 stroke 225 sucks 77 and 35.
A 3.3L Ficht 225 drinks 74 and 40.

From this it would seem that the 225hp Optimax and 210hp V-6 sterndrives use about the same amount of fuel. But then the outboard is at least 120kg lighter, so the outboard could be expected to perform considerably better. This also addresses Mike's concern about the moment of inertia problems with hanging the weight so far aft. The bulk of a sterndrive's weight is located just forward of the transom as opposed to an outboard being just aft of it - but there is significantly more of it so the end result is about the same.

 

Outboards

Thanks for the www.astravan.com link. I was looking for the Bosch unit. I read that the Wolter has been discontinued and I can't find a distributor for the Paloma unit. You need to be very careful to properly vent these units to avoid CO2 poisoning. You also need to be careful of propane leaks.

I prefer the combination diesel water heater and space heater. They are positively vented better and the fuel is less volatile.

The Gland unit is not a 12 VDC water heater. It is a heat exchanger that installs in the cars heater hose.

I don't think stern drives are much better that outboards. The main benefit is the mass of the engine is lower which helps in turning, but as you point out, the pitch moment of inertia is almost the same, weight is higher and corrosion problems are about equal (unless you use the Volvo composite stern drive). Inboards and the surface drives allow you to select the drive shaft length to improve the placement the engine mass. The Arneson dealer told me that they converted a Fountain boat to Arneson drives and were able to eliminate 1,000 pounds of ballast from the bow. Needless to say they experienced a significant performance improvement.

I guess I am used to dealing with more sophisticated customers than the average consumer. I do not think that the average user will use their boat enough to make fuel consumption very significant. I was more concerned with the total cost of ownership. Total cost of ownership is the purchase price plus the associated cost of money, maintenance and operating cost minus the resale value. Military customers won't use outboards (except of RIBs) or stern drives because they know the total cost of ownership is much higher and performance is lower.

Cheers;
Mike Schooley

 

It's an interesting point you make Mike. The 1st thought that springs to mind is that your military customers would choose diesel power where possible because of its longevity and reliability. It makes sense - though as diesel manufacturers pull more and more power out their motors and other manufacturers go higher and higher tech, the difference isn't quite what it used to be.
Yet (in these parts at least) commercial operators overwhelmingly go for outboards. There are a number of reasons for this - downtimes are shorter (simply unbolt one motor and bolt on another), initial purchase price is lower (than diesels anyway) and the costs are tax deductable, so they can replace them every 1 - 2000 hrs for minimal cost. The other reason is that outboard powered boats tend to be much easier to get into - and keep in survey.
Oh, and you're right that Glind unit I've found isn't 12 volt - in fact I've yet to track one down. One boat that I thought used a 12 volt system, was in fact a 240 volt immersion type heating unit, run though an inverter - and only used with the engines running.