Power choice Poll

The Trimax would have seemed a good choice here, but they only recomend using them in twin installations - singles for racing only

 

That's interesting - I didn't realize that (although it sounds familiar now that you've said it). What's the logic? Is there any similar recommedation for Arneson or BPM drives?

 

Not that I know of. I only happen to know about the Trimax's because I spoke with the their people about a pleasure craft application. Pity, because (apart from the price) the Trimax is a rather attractive package. According to Buzzi's people, the system performs well in the "getting onto plane phase" compared to other surface drives. Without going back through my files, I'm not sure why they don't suggest for single installations......

 

Inboards

The stern drives on the Princess V42 are all DuoProp (counter rotating props) which are documented to provide 15% higher thrust than a single prop for a given power level. Since the inboards do not have counter rotating props this accounts for about half of the efficiency difference.

In general, it is a bad idea to compare efficiency at maximum speed because the power : speed curve is so steep. It is better to compare power levels at a common speed near cruise speed. Most diesels are optimized for maximum efficiency at cruise (as opposed to gas engines that are optimized for maximum speed) and since the inboards thrust angle can not be trimmed their performance suffers at maximum speed.

Many manufacturers design their boat around a certain engine and then offer alternate engines as options. The boat is rarely redesigned and re-optimized for the optional engines which makes the optional engine appear to under perform.

In the case of O-1 it is best to compare drive efficiency at 22 to 24 knots as you pointed out in the case of surface drives.

Here is an interesting FAQ from http://www.powerboatguide.com/FAQ/faq.htm "Why is a 27-foot boat with twin 200-hp outboards faster than the same boat with 200-hp inboard engines?

Simple. You can trim outboard engines to gain maximum prop efficiency for speed and conditions. Inboards have fixed shaft angles regardless of speed or sea conditions. Trimming outboards lifts the hull farther out of the water, reducing the wetted surface and drag considerably.

Also, two-stroke outboards are designed for cruising at a higher percentage of maximum rated rpm than the four-stroke gas inboard, and the outboard's horsepower-to-weight ratio is better. It should be said that in rough-water conditions inboard models are generally better designs, as the centralized weight of the engines allows the boat to stay on plane and handle better at much lower speeds than outboard designs."

And another quote from the same FAQ, "I know that engine hours are important, but what constitutes a lot of hours on a particular set of motors?

This is always a hard question to answer, so we'll just offer up some general guidelines. When it comes to gas engines (inboards and I/Os), most dealers and brokers figure those with over 1,000 hours are probably tired. With turbocharged diesels 3,500 hours is a lot of running time, and with naturally aspirated diesels it's not uncommon to pile up 5,000 hours before an overhaul is required.

Unfortunately, a good many of today's ultra-high-performance diesels never see 2,000 hours before an overhaul is required. Sometimes this is a manufacturer problem, but premature marine diesel death usually results from improper owner care and maintenance. ..."

Based on these hours, I'd conclude that the life of a diesel should be 2X to 5X that of a gasoline (petrol) engine. It seams to me that even if you only put 100 hours on your engine per year the resale value of a well maintained diesel would be significantly better.

Cheers;
Mike Schooley

 

Now what? The poll is closed and we have no winner. Do we call the surface drive vote as an inboard vote? Or do we allow this voter to be the tie breaker? We need a call here from a higher authority.
Gary:?:

 

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It appears to me that diesels won but the drive choice is undetermined.

I think the market is just as divided as this forum and we aren't going to settle that question here. To maximize market appeal, I think O-1 should have a gas and a diesel option. To keep the entry level cost low, I think the base model should be gas and the diesel should be optional.

Cheers;
Mike Schooley

 

What time is it in Barcelona? We need Paul to make a ruling.

 

Uh oh - I'm in trouble

I am the one who voted for the surface drive switching my vote from inboard. The truth is I am torn between inboard and outboard if I can't have a surface drive. My head says outboard but my heart says inboard.

 

Ok 1st up to Mike's very good rebuttle of my inboard / sterndrive comparisons. And it is true that the Duoprop is responsible for at least some of the efficiency gain over the inboard. But consider this. I the Sealine example I described, there is a third set of performance figures to take into account. Same boat with a pair of 300hp D-tronic Mercruisers, with Bravo 2 legs (single prop) runs a top speed of just over 30 knots - 1 knot slower than the duoprop with 80hp less, and still only 2 knots slower than the 420hp inboards can manage.
'Tis true that one should probably compare the efficiencies at cruise - at around 28 knots both Bravo 2 and Duoprop consume about 15% less fuel than the inboards. Not as great a difference as one might expect, probably because the smaller diesels in Sealines sterndrive versions would have to work harder.
I would suggest that the difference would be greater in a lighter, more easily pushed hullform (such as O-1)
Now, as for engine life. I would agree that older generation outboards have a "1st life" expectancy of around 1000hrs. But the newer technology 4-strokes and dfi 2-strokes are generally lasting around twice as long. This (at 100 hrs per yr) is at worst 10 years of use and more likely around 20. I think that effectively takes the concerns about engine life out of the equation.

I also don't believe that petrol engines (inboard or outboard) are optimized for maximum (top speed) performance. Most outboards run best at around 4000rpm, with a max of about 6000, or 66%. My 5.7L sterndrive drinks fuel at an increasingly alarming rate when run much over 3600rpm (most economical at 3400) and has a max of about 4400rpm - 77%. Most diesel manufacturers suggest you run at around 75% max rpm - all about the same.

But, as you say - this is somewhat of a moot point, given that our poll has closed without a clear winner!
There seems only two sensible options - we either vote again and hope for a clearer outcome, given that many voted before much debate had been done. Or, with six votes to five, we adopt the inboard (gas or diesel) and then reconsider the driveline options.......

 

Hi all

How about we do a quick re-vote. This time with 2 options

1)Inboard propulsion

2)Outboard propulsion

Any objections?

Paul

 

One thing just struck me as I read this mornings posts on the power poll. One of the last projects I worked on before I retired had a similar problem with reaching design decisions. The project leader decided to do what we have been doing, that is, take a vote on the various elements of the design.

We sat around a conference table and took up the elements one by one and kept score of the votes on a blackboard. I was in the minority in the voting many times.

The product failed miserably, both technically and in the marketplace. I have reviewed this failure several times to try to find why it went so wrong. There were people in these meetings from engineering, field representative, management, manufacturing, packaging, and marketing.

I think one of the crucial problems is that everyone got an equal vote on each item regardless of whether it was in or outside their field of expertise. It also demonstrates the classic committee design scenario.

In the current debate, I voted for outboards. I think they are best suited to the O-1 project AS I VIEW IT. I admit to having far less experience or knowlege of inboards and drive systems than several of you who have provided a wealth of information on these. My vote is intended to keep the boat lighter, more easily trailerable, simpler for the home builder and less expensive.

Perhaps one way out is to make a fundamental decision between the above goals and inboards. That is, use inboards and drop the easily trailerable, simple and less costly objectives -- or--- go with outboards and go to the smaller lighter simpler end of the range. Perhaps the original concept got driven to the high end and is no longer ideal for either power plant.

Anyway I think we are stuck with the committee vote process by the medium we work in. We are learning a great deal and it is very useful but we should not take the end product too seriously.

 

Poll

Will;

My point on the speed of gas versus diesel is not the speed of the engine, but the design speed of the boat. Most diesel customers are interested in fuel economy and range, so builders tend to prop and trim the diesel configuration for efficient cruise speed. OTOH most gas customers make their comparisons based on maximum speed, so builders prop and trim the boat for that.

At a boat show I stopped to look at a boat with gas or diesel engines. My first question was what is the range. The sales rep immediately assumed I was interested in the diesel engine option. When I asked how he knew I wanted diesel he said, "because you asked for range and not how fast will it go."

Although this is a lot of fun and I am learning a lot, I think we are splitting hairs. There is no best option because the best choice depends on the customers application.

I think the design committee process often fails because there are certain decisions that tend to go together and certain decisions that just don't. Some decisions need to be made as a group, or based on their impact on the rest of the system. Like a hot shower and an outboard, you need to add in a water heater and a expand the battery bank and add an inverter. If the committee doesn't have strong leadership and insight the process is destined to fail.

I see the propulsion choice as two interrelated decisions. First is engine choice; gas, gas or diesel or diesel only. Of course the diesel options eliminates outboards. The other choice is drive; outboard, stern drive, inboard, surface drive or jet. Maybe we should have two separate parallel polls, one for engine and one for the drive. OTOH we would probably choose diesel and outboard.

Cheers;
Mike Schooley

 

If this is the cheap version then it should have the cheaper power. I was for diesel but that should be for the higher priced one. Right?

 

Diesel

Yes, but you need to design around the heavier weight option. Since diesel is generally heavier I think we should design to that and then putting a lighter weight gas engine in would be easy.

The main think is to keep the diesel option open. If O-1 can only accommodate gas engines then you loose the diesel market.

Cheers;
Mike Schooley

 

So you want to have two power types for the boat right?