Gimme Power !!

[Willallison]

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......

[duluthboats]

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 :D) 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

[Portager]

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

[Willallison]

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.

[tom28571]

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.

[duluthboats]

:D :D :D

[Portager]

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

[tom28571]

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.

[Portager]

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

[Jeff]

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.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.

[Jeff]

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?

[duluthboats]

2 sites with LP marine water heaters.


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

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

[Willallison]

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.

[Portager]

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

[Willallison]

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.

[Portager]

I've thoroughly researched all the drive options (I can think of) for O-1 and I would like to recommend the "Power-Vent" surface drive. http://www.powervent.com Power-Vent is a surface piercing drive, like the Arneson drive, however it is mounted completely under the stern in a vented tunnel. The vent is connected to the stern via a separate tunnel and is cleverly designed to provide speed compensated ventilation to the surface piercing propeller. In this way the drive requires no driver intervention as speed and conditions change and the flex couplings and hydraulic actuators are eliminated.

Here is a report that the Naval Surface Warfare Center Carderock Division filed on a test of the Power-Vent drive. http://www.powervent.com/navyreport.html. In this test, the maximum speed obtained during the trials was 40.5 kts (46.6 mph). More recent test reports show that they have increased that to 51 mph. http://www.smithboats.com/robb_report.htm You will note that the recommendation of the Carderock report was to acquire a prototype boat. As a result of this report a 40' boat driven by a Power-Vent surface drive has recently been acquired. http://www.powervent.com/APTD.html it was delivered in January 2002. http://www.smithboats.com/military_police_craft.htm. I should be able to obtain a copy of the on-going test results on this boat when they are complete.

Another informative article on Power-Vent was written in Popular Mechanics http://popularmechanics.com/outdoors/boating/2000/6/Scratching_The_Surface/. An interesting paragraph reads, "Real-world testing of Power-Vent was done by George Boynton, founder and then president of Shamrock Boats. He installed a Power-Vent system in a Shamrock 31 sport fish. Powered by twin Crusader 454-cu.-in. 330-hp engines, the boat had a measured top speed of 45 mph. Modifying the hull with Power-Vent saw the top speed jump to 52 mph--an increase of 15 percent. Fuel efficiency at 35 mph cruise speed went from 1.25 mpg to 1.5 mpg--a 20 percent gain." These results are on the low end of the range the improvements demonstrated by conventional surface drives. If these results were achieved on O-1, we could achieve 15% higher speed that an equivalently equipped "Express Cruiser", or we could achieve comparable speed with a smaller engine.

Here is a summary of my findings:
Performance: significantly better that stern drives, inboards and outboards(?) almost as good as conventional surface drive
Cost: Lower than surface drive close to inboard
Corrosion resistance: Comparable to inboard and surface drive better than stern drive and outboards.
Mass properties: Heavier than outboards comparable to inboard lighter than stern drives and surface drives. Greater flexibility in longitudinal CG that outboards and stern drives. Better vertical CG that outboards.
Engine flexibility: can accommodate either gas (petrol) or diesel engines, either raw or fresh water cooling, interface to water heater.

The main disadvantage are the Power-Vent must be integrated into the hull and the engine must be located further forward.

Cheers;
Mike Schooley

[duluthboats]

I remember reading about them. Great idea, but it would eat up some space. Can we just take this idea and use it, or will we have to pay a user fee.

Garyhttp://boatdesign.net/fimg/powervent9.jpg

[Willallison]

Gary,
I believe that you simply buy the power vent system in the same way as you would buy any other drive system - though the hull must be designed specifically to take the unit.

As you may have noticed from a number of my other posts, I'm a bit of a fan of surface drives - but (ain't there always one of them!) they bring up a number of other issues.....
1st up, we've elected to give O-1 a max speed of about 28 knots. From memory, I think Twin Disc suggest that the Arneson surface drive becomes more efficient than other drives above 35 knots. The power vent is probably similar.
2nd you are unable to trim one of these drives up. That means riskier shore landings (though better than with conventional shafts). It also makes cleaning debri, or changing props are much more difficult job.
Lastly, I'm not so sure that I would agree with Mike about the corrosion resistance. Outboards these days have sufficient trim to enable them to be lifted completely clear of the water - zero corrosion problems. And remember that O-1 is not likely to be left in the water for lengthy periods of time anyway.

Aside from all that, I really look forward to seeing the results of the tests of this unit - and as I said, I love surface drives, so I'd love to be convinced that it was the unit for O-1......

[Willallison]

When in doubt, ask someone who knows....
I've emailed Powervent and asked them whether their drive would be appropriate for a boat with a top of about 30knots and able to operate efficiently on plane down to around 15.
Hopefully I'll get a reply soon.

[dweymer]

Hi all...as for outboard vs. inboard/stern drive, I think I may have a simple(albeit silly ) suggestion: the "average" express boatbuyer desires inbd/stern drive over outboards so that they can swim off the back without dodging the motors/props...plus, a swim platform makes a nice place to cookout at the slip.:D

[Jeff]

First, welcome to the forums dweymer! I think the appearance and functionality of the transom certainly is a large part of it. Will posted one solution to this which I had not seen before where a hinged portion of the swim platform lifts with the outboard. I'm not sure how large a section this would be practical for, but it seems like an option. http://forums.boatdesign.net/showthread.php?s=&postid=2521#post2521

[Portager]

In regards to the speed, I think your on the right track contacting Power-Vent. I e-mailed them yesterday but have not received a reply yet. Arneson and Twin Disc both told me surface drives are more efficient at all speeds above planing because the drag is lower and the mechanical losses in the drive train are lower. The data I received from Twin Disc (and haven't had time to report on yet) supports this. One comparison Twin Disc provided involved changing a "fixed surface drive" on a 26' "Sea Skimmer" tunnel hull. Cruise speed, defined as 2700 rpm, increased from 27 mph to 33 mph and fuel consumption at cruise went from 10 gph to 8 gph. This represents a 20% improvement in fuel consumption rate but a 51% improvement in mileage, from 2.7 mpg to 4.1 mpg. Twin Disc also retrofit a 100' Camcraft which was converted from a supply boat to a Yacht. The engines were reduced from three 600 HP engines to two 650 HP engines. Cruise speed went from 24.3 knots to 23.7 knots with a 28% power reduction. Fuel consumption went from 100 gph to 72 gph. In the table of military applications they list a 26' Uniflite Survey Craft with a speed of 24 knots, a 70' Boghammar landing craft with a speed of 25 knots and a 50' Bristol patrol boat with a speed of 28 knots.

On corrosion, keep in mind that outboards are salt water cooled and they have dissimilar metals. Many inboards are fresh water cooled and have no dissimilar metals. Surface drives are stainless steel with zincs. While it is true that most trailerable boats are kept on the trailer, O-1 is also intended to spend a week at a time on the water. Outboards will require a fresh water flush after use which will probably not be performed each day.

You have a good point about trimming the drive for a beach landing, but I didn't see that requirement in the requirements list:). The Power-Vent saves a lot of cost and complexity by eliminating the need to trim the drive.

Another disadvantage of Power-Vent that I overlooked is low speed maneuverability. You can not vector the thrust and surface piercing props do not reverse very well.

Cheers;
Mike Schooley

[Willallison]

I'm not too sure that the PowerVent would suffer from the often discussed low speed manouvering problems faced by surface drives.
The problem faced by a number of systems - those such as the Arnesons on your Magnum - is that the reverse thrust from the props is directed straight into the essentially vertical transom. The section drawing of the PowerVent shows hull cutouts which should allow this thrust to pass under the boat, so I would imagine that it would be ok in this regard.
It's interesting to see the variety of applications for the Arneson's - and many of those you've noted fall within the performance spectrum of O-1, with its expected top of about 28 knots. But you will also note that most of these are commercial or military boats - designed to operate continiuously at a given service speed. O-1 must be efficient throughout its speed range in order to be succesfull - ie from about 12 knots to about 28. I'm yet to be convinced whether the surface drive is capable of this.

[Portager]

Your explanation of the Magnum reversing problem makes sense. I hope your right about the Power-Vent reversing better.:)

I only listed the models that were <=28 knots. There were a lot more that are >28 knots.

The military patrol boats tend to operate for very long periods at patrol speeds which are typically 12 to 18 knots depending on sea states. They only operate at maximum speed when trying to overtake someone or when responding to a rescue request. It is true their hardest requirement is generally maximum speed, but they are also very concerned with cruising range/endurance.

What Twin Disc and Arneson told me is that the surface drive is more efficient that conventional drives (specifically outboards and stern drives) at all planning speeds. Below planning speed they are claimed to be equivalent to a conventional drive. I talked to our boat driver and he confirmed this.

I think the best input would be from some Power-Vent customers. I know some guys at NSWC Carderock. I'll see if they have any feed-back on their Power-Vent boat yet.

I'd like to do some cost comparisons for the different drive options. I'm a little concerned about the cost of the Rolla surface piercing prop. What horsepower range do you think we will end up in?

Cheers;
Mike Schooley

[Willallison]

Many outboard / sterndrive owners carry spare props, so that in the event of damage it can be quickly and easily replaced. Also it allows for a change in pitch to suit varying loads / conditions.
The cost of the rolla, or similar props is only 1/2 the problem: their availability could be a problem also.
From what I can gather, prop selection is vitally important to successful surface drives. And overloading the boat can render a surface drive virtually inoperable. These could all pose problems for the amateur builder.

[Willallison]

As far as hp requirements are concerned, Tom recently posted the following numbers:

90hp = 24knots
115hp = 28 knots
150hp = 32 knots

ie we're definitely at the bottom end of the surface drive power spectrum!

[Portager]

I found an article titled "Surface-Piercing Propellers
by Paul Kamen, N.A." http://www.simplicity-marine.com/surfprop.htm which I thinks answers the question of the application of surface drives to moderate speed (i.e. 28 knots max) planing vessels.

The entire article is quite interesting and informative, but the part that is the most applicable to O-1 is, "Surface propellers have long been accepted for racing applications, where minimizing appendage drag and cavitation are the major motivations. In recent years, an increasing number of high-speed yachts and patrol boats have been propelled by surface propellers, and some of these applications have been spectacularly successful. But the use of surface propulsion for relatively heavy and slow vessels is new."

Cheers;
Mike Schooley

[Portager]

I called Paul Kamen (Paul Kamen <mailto:pk@well.com> is a naval architect with degrees from Webb Institute of Naval Architecture and the University of California at Berkeley. Formerly the Applications Naval Architect for Arneson Marine, he is now an independent consultant specializing in surface propulsion.) and discussed the O-1 project with him. He said that at the speeds that O-1 is designed for we would probable see a small increase in speed over a submerged drive for a given power level. He didn't know how much of an improvement the surface piercing drive would provide, but he indicated it would perform better than a submerged drive.

He said that Simplicity acquired the article that he wrote and added their name. His original article is at http://www.well.com/user/pk/SPAprofboat.html you can also down load a program that he wrote while he worked at Arneson to analyze surface drive craft at http://www.well.com/user/pk/SPA.html

This program should provide a fairly good estimate of O-1 performance with a surface piercing drive.

Cheers;
Mike Schooley

[Willallison]

What's that they say about great minds?.......Poor old Mr Kamen must be wondering what's going on - I emailed him to discuss the O-1 project and another that I am working on !!
I have actually seen his article reproduced in a number of places - pitty he probably doesn't get royalties for such use!
As you say, he could see no problem with the use of a surface drive. I mentioned my concerns with the requirement to perform over a wide performance spectrum and he made no reference to this in his reply, so I think we can safely assume that it should pose no problems.
But given that the surface drive is only likely to yield a small perforomane benefit, it can't be said to be so much better than the alternatives to render them not worthy of consideration. It also means that the surface drive definitely IS worthy of consideration.

[Portager]

I agree with your conclusion. The surface drive is just one of the options. I'm collecting comparison data on outboard, stern drive, surface drives and ?

I also called Power-Vent today. I talked to their sales manager (if you can call the head of a one man department a manager) and their application engineer. They both tried to convince me that O-1 wasn't a good application for a surface drive. When I pressed them on this they admitted that they had only tried one moderate speed vessel (a Sea Doo conversion) and they admitted that they had the gear ratio wrong. I concluded that for moderate speed applications it is critical to optimize the prop diameter and gear ratio for the intended speed like Paul recommends. If we do end up selecting a surface drive I think we would be wise to seek professional help. I also decided that the "Power-Vent" may not be the best surface drive option.

Cheers;
Mike Schooley

[Willallison]

I've done a little research as far as the hot water system issue is concerned for outboard powered boats.
It seems that if you want to avoid the use of gas (lpg etc) - which is a good idea in any petrol engined boat - then the only real option is to go for a 240 / 120 volt immersion style heater run via an inverter when the engine is running.
At first this seems a little awkward, but if you consider the choices made for inboard powered boats, the end result isn't vastly different. Most hw systems operate on high voltage when the vessel is connected to shore power (or generator) or through a heat exchanger when the engine is running, so you can still only generate hw by running the motor when you're away from the dock. And in my experience, in commercially made units, the immersion element is a more effective heater than the heate exchanger anyway.

[Nomad]

Could someone give me a quick summary(ex. speed, power), you Guys left me behind. WAY WAY BACK!! Thanks in advance...........

[Nomad]

I REALLY miss starting topics(being a captian or atleast a Co-Captian)

[Willallison]

Nomad, as requested - speed choices made so far:

1. Max speed 25 - 28 knots
2.Max Cruise 20 - 22
3. able to maintain planing down to 12 knots and economical to operate throughout its speed range

Later we could give consideration to the GTi Expre$$ version.

[Nomad]

Thanks Will you have been a big help today!! :)

[Nomad]

Just noticed that the planing speed is approx. the same as the "ORCA" 31' and 36'.

[Boghammar]

regarding the Boghammar boats u mention. One of our boats that is more known is the type we built to Iran. A 13 meter long patrolboat with "second effort" Surface drives, doing roughly 60 knots.

Best regards
Wilhelm Boghammar

[Willallison]

Hmmm - show us pics Wilhelm!

[CORMERAN]

Portager,

pure engineering doesn't apply neccessarily - to marketing or building
recreational boats.

Builders, concerned with man hours, love stern drives. Because you
just cut a round hole in the flat part at the back of the boat - glass in
something to bolt the engine too - and you are ready to shove in the unit.

Also wiring up the inboard - usually goes pretty quick.

Conversely, I have spent DAYS - installing an O/B bracket and getting
all the wires in place, in a sanitary and shipshape manner.

From a design point of view - beyond 18' - outboards become harder
and harder to justifie.
- Because the bigger they get, the less seaworthy, generaly - things become.
- Also - the stresses on the transom can be of concern. As weight and
H.P. escalate.
A client once asked me to design a vessel that would have had FOUR !!
giant outboards - hanging in space - off the end of his boat.

I refused to do it.

Subsequently, a race boat rigged this way - lost it's transom.
- And the FOUR giant O/B's on it .......and then quicly the boat sank as well.

There are sound engineering reasons - for inboard installations.