Power choice Poll

Now I need to get up to speed on water jets - cost and performance vs. surface drives at these speeds.

Also I wonder if diesel + surface drive will simply stretch the budget too thin as both are big ticket items.

 

Re surface drives,
I've just had a reply from propulsion alternatives ( http://www.propulsionalternatives.co.nz/ ) to a request about their suitability for a project like O-1. In part, it reads:

It is quite feasible to use a surface drive on this application and still
get the efficiencies you are after, but there are some careful design
considerations that must be accounted for.

Typically surface propellers are not as efficient as submerged propellers up
to speeds of about 35 knots. Having said this, the reduction in appendage
drag and the ability to use larger diameter propellers on the surface can
over compensate the inefficiencies. By using the correct application, and
of course the correct hull design and applying the correct power option, it
is possible to use surface propellers very effectively at these speeds. It
is certainly also possible, again with the correct application and biota
design to retain low planing speeds and even carry heavy loads.


As soon as I can get some more info, you'll be the 1st to know....

 

8knots not all diesel inboards are slow I have done a few that have topped 40+ knots! Not to bad no?

 

'nother reason for outboards over diesel - price. You can by the latest in o/b technology for less than 1/2 the price of a diesel. With a 50K budget, this has to be considered.....

 

Yep on the cost factor!

I was at the time not aware of the speed range chosen for O-1
Now i will reconsider the options..... I think outboards are the answer for this project "ease of install, cost, power to weight ratio and most of all 28 kts is cake to a modern 4 stroke! 8

 

Gas versus Diesel

I think O-1 should be gas with a diesel option. Then the people who really want diesel can pay extra for it, however to accommodate the diesel option I think you need to design around the diesel from the start.

I think the cost of outboards is very deceptive. What is the typical life of an outboard engine versus an internal gas or diesel? Outboards are essentially disposable engines. I have read that the investment that one makes in diesel engines is returned at the fuel pump, in maintenance costs and in resale value.

Look at the cost of the same make and model of used boats with gas and diesel engines. The diesel will hold its value much better.

Where is the data? We are making decisions based on polls and nobody is presenting any hard data. Everybody says outboards are cheaper, not nobody presents numbers.

We are never going to settle the gas versus diesel debate. My question is do we want to design a boat that can only accommodate one side of the argument?

Cheers;
Mike Schooley

 

Fine you guys won me over(If you cant beat them....) I'm with Outboards

 

Engine Options Data

OK, since I keep winning about comparison date, I did some research and make some calls. Here is what I have so far.

Tom's data shows that 115 HP will allow us to just meet our maximum speed goal, but this early in the design, I think we should have some margin, so I concentrated on engines around 150 HP.

Mercury Saltwater EFI 150 outboard
http://www.mercurymarine.com/cgi-bi...100@@@@&BV_EngineID=gadcehckljfibedcfececjf.0
150 HP, weight 416 lbs, displacement 2.5 liters, max RPM 5000-5600, 60 degree V6, Shaft Length: 20 in. , Alternator: 40 amp, MSRP $12,266, phone quote $12,273 Refurbished 2001 $7,499 60 Day Mfr. warranty http://www.boatmotors.com/rebuilt_outboard_motors/

Mercury Mercruiser 135 stern drive
http://www.mercurymarine.com/cgi-bi...100@@@@&BV_EngineID=gadcehckljfibedcfececjf.0
135 HP, weight 623 lbs, alpha drive, displacement 3 liters, max RPM 4400-4800, inline 4, L 34", W 23", H 20", Alternator: 65 amps

Mercury Mercruiser D2.8L D-Tronic inboard
http://www.mercurymarine.com/cgi-bi...100@@@@&BV_EngineID=gadcehckljfibedcfececjf.0
Propshaft HP 150 HP, weight 1,016 lbs, displacement 2.8 liters, max RPM 3600-3800, inline 4, L 49", W 28", H 21", Alternator: 65 amps

Steyr diesel 164, http://www.steyr-motors.com/products/products.htm
163 HP, weight 568, displacement 2.13 liters, max RPM 3800, inline 4 cylinder, L ", W ", H ", engine and trans retail $20,300, quote from http://www.laudiesel.com $11,438 + drive shaft, bearings, seals, propeller, ...

Simplicity Surface Drive SMD 100, Marine Power 262 V6, Hurth 450A,
166 HP, weight 730 (engine) + 62 (trans) + ? (SMD 100) = 792 + ?, displacement 4.3 liters, max RPM 4300-4600, V6, L ", W ", H ", $10,337 http://www.simplicity-marine.com/mpower.htm#Mpower, spare prop $1,670 http://www.simplicity-marine.com/propeller.htm

Simplicity Surface Drive SMD 200, Yanmar 4 LHA-HTA Turbocharged with Intercooler, Hurth ZF-63, 170 HP max 154 HP continuous, weight 895.1 (engine) + 101 (trans) + ? (SMD 100) = 996.1 + ?, displacement 3.455 liters, max RPM 3,300, Inline 4, L ", W ", H ", $20,054 http://www.simplicity-marine.com/yanmar.htm#Yanmar spare prop $1,670 http://www.simplicity-marine.com/propeller.htm

I think the Steyr is the best diesel engine choice for O-1. It is lighter weight than many gas engines of the same power so there is no weight penalty for the diesel option and the engine has a very attractive price. The Steyr is a very advanced engine. It has a monoblock engine which eliminates the head gasket and head joint (saving a lot of weight) and variable geometry turbo charger. It is said to be very smooth running and very little smoke. Mean time between overhaul (claim) is >7,000 hours. With a Simplicity surface drive the Steyr would be about $16,500.

Here are some reviews that I thought some of you might find interesting.

Outboard review;
http://popularmechanics.com/outdoors/boating/2000/8/Five_Outboard_Motors/
These are smaller outboards that O-1 would need, but some good comparison data.

Gas stern drive versus diesel stern drive test;
http://popularmechanics.com/outdoors/boating/1997/10/Mercruiser_vs_Mercruiser/
These are much larger engines that O-1 needs, but I think it is interesting to note the difference in weight, cost and range. On identical boats and the same volume of fuel the gas had a max range of 149 mi @ 28 mpg versus the diesel max range of 261 @ 26 mph.

Cheers;
Mike Schooley

 

Ok, some numbers:

These are the list prices from my local maercury dealer, are for the package NOT INSTALLED and are in Australian $:

Mercruiser D2.8L Dtronic diesel inboard, with down angle g/box, $30,346

Same motor with a Bravo1 sterndrive, $33,017

150hp Optimax x-long shaft, $17,970. I use this engine as it is the most expensive, most high-tech they make in this power range.

Merc do not produce a petrol inboard in this power range (does anybody?), but their 135hp, 3L sterndrive (Bravo1) comes in at $13,852.

The optimax o/b, will at worst, very nearly match the diesel inboard for fuel economy and would outperform it in every other respect, given its lighter weight and the inefficiencies imposed by the shaft angle, appendage drag etc.
Most owners would struggle to put 100hrs a year on their engines and many would put less than 1/2 of that. The life of the Optimax, before any major work is required should exceed 1500hrs ( I know of a local commercial operator with over 2000 hrs on his and has experienced no problems). So at worst you could expect 15yrs of trouble free running. True, the diesel could (if properly maintained) quite easily double those figures, but given the $12,376 price difference, the owner could almost afford to replace his o/b after 10yrs or so for the same money.

 

My choice of an outboard is driven by a couple of perferences.

1. For myself I only want a boat that is light enough to trailer easily and care for in my own yard.

2. I also want a light boat for economy of operation and economic performance.

3. I am happy to make the sacrifices of showers with water heaters, air conditioners, standing headroom in the sleeping cabin (but no in the pilothouse) and any other supposed creature comfort that impacts too much on number 1 & 2.

4. Since I don't need to travel at 35kts, a smaller lighter engine will fit best with number 1 & 2.

5. Since my boats are all one-off, I have no desire to expend limited time and energy in designing, debugging and installing a proper power system and am willing to accept the completely engineered package that can be had with an outboard.

In my admittedly limited study and experience I have concluded that I can best satisfy number 1, 2, 5 & 5 with an outboard of modest power and weight.

I sense that mumerous people have other slants on the relative importance of all these factors. So, for the time being I going to simply try to learn from the expertise of others on some of the different power systems and keep my prejudices in check (maybe).

I would question the costs of the different systems that Mike gave in that the outboard costs are real and need only added tax and a small installation charge. Any inboard installation is much more open ended and the discovery of all the problems and associated costs in getting a boat to meet its goals has been the undoing of many professionals, not to mention amateurs.

In gas engines, I'd want to look at the Mazda rotary for its small size and simplicity. In diesels, I have no clue since I've not seen any installations that could meet the goals we have set. Not to say that they aren't out there but I have little experience with them other than using diesels on sailboats and semi-planing powerboats.

On the hard data issue, I posted several examples of numbers but have had no direct feedback and almost no discussion. This is only related to hull design since several people have offered some data on power systems.

I suspect that many have been learning from others during the various discussions, so I'm not concerned that we have made little direct progress in developing the boat so far. The electric wheel discussion is good and may be a viable power system but not for our boat. Trouty's Scaler Magnetoelectric drive is interesting but too far over my head right now. I've downloaded the articles but have not been able to make my way through them yet. It still sounds like alchemy at this point. My approach to all perpetual motion schemes has been to wrap them in an envelop and apply the principal of conservation of energy. They have all failed the test so far. Maybe the light will shine by and by.

 

Which data were you referring to Tom, perhaps we should look at it now.....
Never one to be backward incoming forward, I'd be more than happy to give my impressions

 

Alas, it appears I have fallen victim to my own research
I've been hunting around a bit to find the best hot water system that would be suitable for an outboard powered boat. Previously I've suggested the use of a 240 / 120 volt immersion style heater run through an inverter, when the engine is running.
But a little maths seems to render this option a no-goer. Whilst many outboard alternators are capable of putting out up to 60 amps, it is unlikey that they would be capable of doing so for an extended period of time. A 1500w water heater takes about 5 minutes to heat 1 litre of water to "shower temperature", so would take at least 20 minutes to heat just enough water for a frugal boater to wash. And whilst a 60 amp alternator can theoretically float such a drain, in reality it isn't designed for this kind of extended output, so would fail much earlier than it should.
Further, in order to manage this outpouring of power from the battery supply, you should use a number of large capacity batteries to avoid plate damage - there goes the weight advantage of using the outboards in the 1st place.

But a solution is never fat from sight! Whilst I'm not a big fan of using gas (lpg / propane) onboard petrol engined vessels, if the boat is designed to safely house such a supply from the outset, then it is an acceptable compromise. Bosch produce a range of tankless water heaters ( http://www.astravan.com/specs.html ) which would serve the purpose admirably. They are light, simple, effective and inexpensive.
The other alternative, which begins to make sense if you are going to spend extended periods of time at anchor, or making short trips which are not long enough to recharge your batteries properly, is to have a small, lightweight, petrol engined generator. These tend to be much quieter than their diesel cousins. They are also smaller and much less expensive to buy. This would allow the use of immersion or electric tankless style heating systems and open up a whole host of other possibilites as far as onboard electrics are concerned - heaters, air con etc......
The gas alternative is the lightweight choice, the generator the comfort choice......

 

Data Analysis

Using the exchange rates provided at http://www.xe.com/ I got a conversion rate of $1 AUD = $ 0.565890 USD


Mercruiser D2.8L Dtronic diesel inboard, with down angle g/box, $30,346 AU = $17,172 USD

Same motor with a Bravo1 sterndrive, $33,017 = $18,684 USD

150hp Optimax x-long shaft, $17,970. I use this engine as it is the most expensive, most high-tech they make in this power range. = $10,169 USD

Merc do not produce a petrol inboard in this power range (does anybody?), but their 135hp, 3L sterndrive (Bravo1) comes in at $13,852. = $7,838 USD

The Steyr 164 HP diesel is $11,438 USD = $20,212 AUD

Simplicity Surface Drive SMD 100, Marine Power 262 V6, Hurth 450A $10,337 USD = $18,267 AUD

I like you Will, but I can't let you float an unsubstantiated claim like that through my sites without firing the torpedoes!

Since Mercury won't publish their specific fuel consumption data I had to estimate it. According to Boating Life magazine http://www.boatinglifemag.com/BL_Main/1,1675,1-1-1-10877-157-135,00.html "On average, an in-tune four-stroke gasoline engine will burn about 0.4 to 0.45 pounds of fuel per hour for each unit of horsepower. Likewise, a well-maintained two-stroke outboard burns nearly 0.6 to 0.8 pounds of fuel per hour for each unit of horsepower it produces. These figures apply to carbureted and fuel-injected engines, but not to direct-injected engines such as Mercury's OptiMax and OMC's FICHT models. " but this does not provide the BSFC for OptiMax. Using the Popular Mechanics review http://popularmechanics.com/outdoors/boating/2000/8/Five_Outboard_Motors/print.phtml and assuming the 3500 rpm data is close to the optimum the fuel consumption of the 4 cycle engines is 4.0 and 4.1. If I take the conservative assumption and assume the best engine is at the low end of the range i.e. 0.4 lb/HP hr and scale the OptiMax 0.4 * 4.5/4.0 = 0.439 lbs/HP hr converting to gallons per hour with a density of 6 lbs/gal produces 0.0731 gal/HP hr. The Yanmar specific fuel consumption is 185 g/HP hr = 0.407 lb / HP hr using a diesel density of 7.1 lbs/gal yields 0.0573 gal/HP hr. The Steyr specific fuel consumption is 210 g/HP hr = 0.462 lb/HP hr = 0.065 gal / HP hr. The Yanmar fuel consumption rate is 27.7% better than the Mercury Optimax and the Steyr fuel consumption rate is 12.5% better. Notice even though the assumed Optimax BSFC (0.439 lb/HP hr) is lower than the Steyr (0.462 lb/HP hr) the volumetric fuel consumption of the diesel is lower because the density of diesel is 7.1/6 = 1.183 or 18.3% higher than gas (petrol).

If the diesel is driving a surface drive it should be 10 to 15% more efficient that a outboard drive.

If the diesel is at an 18 degree down angle then the horizontal thrust vector is cos(18) = 0.95 or you loose 5%.

The Yanmar weighs 996.1 versus the OptiMax 416 or 580 lbs. For O-1 this would be about a 10% weight increase so the net result, with the surface drive the Yanmar would be 1.277 * 1.1 * 0.9 = 1.26 or 26% better fuel efficiency than Optimax and with an inboard 1.277 * 0.95 * 0.9 = 1.092 or 9.2% higher fuel efficiency than Optimax.

The Steyr weighs 568 versus Optimax at 416 or 152 which would increase O-1 3%. Net result with a surface drive the Steyr performance is 1.125 * 1.1 * 0.97 = 1.114 or 11.4% better than Optimax and as an inboard 1.125 * 0.95 * 0.97 = 1.037 or 3.7% better than Optimax

Since the diesels have 10% higher power that the OptiMax, I think the diesels will at least match the outboard performance.

The cost of the Steyr is $11,438 versus Optimax at $10,169 or $1,268 (USD) more. This represents a 2.5% increase for O-1. Granted this cost does not include the drive shaft, bearings and prop, but the cost difference is not that great.

The effort and complexity of installing an inboard engine is insignificant compared to the effort required to build O-1.

Cheers
Mike Schooley

 

Thought I'd get a rise out of that one!!

Consider this from an earlier thread:

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 225hp 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.


In particular note the 225hp Optimax consumption. At wot it is consuming 66 Lph or 14.5 gph. ie 0.065 g/hp/hr.
You quoted the Steyr as consuming 0.065 g/hp/hr - exactly the same!

One area where diesels have traditionally had it over the alternatives - and particularly outboards is at slow revs. A diesel's consumption tends to be essentially linear - the slower you go, the less fuel you will use in mpg terms. Older technology o/b's are almost the reverse, at displacement speeds they'd throw fuel out the exhaust almost as fast as you could pour it through the carbies. This is where my enthusiasm for Optimax comes from. Our own boat, with one its 225's pushing it at 6knots uses just 3 Lph - or 9 nmpg. I believe this is as good, or better than a diesel of similar power could manage and way better than any inboard petrol engine would do.

You will recall my enthusiasm for the surface drive concept - and all the creditable evidence does lead to a 10 - 15% improvement in efficiency as you say - but only at speeds over 35knots. At less than this, most information I have seen suggests that the surface drive will only match the alternatives. It also doubles the cost of the engine installation, so will probably not fit our budget.

I can't argue with the maths, but I'm not too sure that the results are born out in reality. I have a number of tests at home with direct comparisons between shaft drive and sterndrive powered boats. The efficiency of the sterndrive is essentially the same as the outboard, so the comparisaon is a valid one. I'll dig them out and post them asap


ps. I like you too Mike!! and I look forward to the response which I am sure will be forthcoming!!

 

Math

Nice argument except 1 liter = 0.26417205235815 gallons, therefore 66 lph = 17.43 gph i.e. 0.0775 g/hp/hr which is worse than the 0.0731 gal/HP/hr that I used.

The information that I have indicates that above 35 knots the difference is ~30%, below 35 knots it drops to 10 - 15%.

If you look at the "Stern to Stern" comparison http://popularmechanics.com/outdoors/boating/1997/10/Mercruiser_vs_Mercruiser/ that I posted earlier I think it shows the results are born out in reality. Even though the diesel was 272 lbs heavier and 10 HP lower power, it provided slightly higher speed and significantly better fuel economy.

I'd like to see some real numbers on this and take into account the cost and installation cost of the water heater.

Cheers;
Mike Schooley