Help me make the decision ... twin or single diesel?

[piperca]

I am getting close to getting back into my boat project, since my home remodel is getting close to completion ... :)

I have a 28' Skipjack Flybridge that I have removed the twin gas engines from and am now considering repowering with diesel(s). My dillema is twins or a single. I am considering either a pair of rebuilt Volvo Penta AQ31P-As (one is actually new) or a single rebuilt Yanmar 6LP. The Volvos are 150 hp each and the Yanmar is 315 hp. Price to install either is not an issue, since it works out close to the same ... couple of thousand more for the single.

Yes, it would be a lot easier to drop twins into the current setup and use the existing outdrives, but I'm looking at maintenance, also.

There's a bunch of transom patching and stringer reconfiguration to take place if I do the single. I'm a carpenter by trade, so that doesn't really scare me too much, I'm just a little burned out with remodeling projects, I guess.

Anyway, given the options, those of you that have experience with this type of work; which way would you go? Why/why not?

I have a terrible time making up my mind, so anything you guys can throw at me would help immensly!

[El Sea]

FWIW:
Since I favor the single engine concept, I would go the Yanmar, this would be a good time to get those stringers and transom in shape.

If you were determined to go twin, I would go a pair of smaller Yanmars, I really don't get a true, warm fuzzy feeling when it comes to Volvo's.

Luther Carrier
Absolute Tank Cleaning
St Petersburg, Fl

[piperca]

Thanks for the response!

Do you have experience repowering from twins to a single? I am wondering how this would affect the boat, since it was designed to be run with twins? The guy who is going to do the install thinks that a single is a bad idea; he thinks it will affect the boats center of gravity in a negative manner, since it is an 8' beam and is tender on the drift with twins ... comments?

[El Sea]

I would hope that when the twins are removed along with the shafts, struts, etc a keel would be layed to give stability and protect the prop/shaft.

Keep in mind with a 8' beam and twins, how are you going to maintain them?

[piperca]

Sorry, I should have clarified; the boat had twin I/Os (sterndrives), so there's two lovely big holes in the transom that will need filled! Here's a pic of what I was left with:

http://i275.photobucket.com/albums/jj316/piperca/P4060004.jpg

[mydauphin]

The boat was design for twin stern drives gas engines. The new diesel engines will probably be a lot heavier (first Problem). and if you don't use stern drives what other type of drive are you going to use. You don't have room for much.

I would go with single diesel, surface drive.... Save a alot of work with rudders etc... Check out Levi drives and you dont have to open holes in bottom.
I had a 8 foot beam with twin engines, what a maintenance nightmare.

[piperca]

Yes, weight was an issue, but I decided on Volvo Penta 31s, which are very close to the weight of the small block Chevys. Now, if I were to go with a single, I'd be dropping close to 1000lbs ... nice thought!

Surface drive? I am not familiar with this type of drive; heard of it, but know nothing about it. Can someone guide me to where I might learn a bit about them (installation, maintenance, etc.)?

And, yes, I have learned that the twins are a maintenance nightmare and would like to leave that behind!

BTW: I was just looking over some information on these surface drives. How do these drives perform in a fishing environment? Do they become a bit of an obstacle when fighting a fish? They appear to hang pretty far off the stern ... am I wrong about this?

Update: I don't think the surface drive will work for me. According to what I've read, they are not preferred for slow speed, like the speeds during trolling, etc.

[CDK]

The difference in weight between a small diesel and a gas engine is no issue, certainly not when you contemplate changing from stern drives to surface props.

Admittedly, maintenance on 2 engines takes more money & time than one, but having two engines makes a lot of difference in handling your boat in narrow spaces, crosswinds etc. And in case of a defect or prop damage, it can make the difference between getting home by yourself or waiting for a tow.

I changed from stern drives to jets, then after 2 years of jet misery to tunnel drives. Took lots of time and resources, but it was very rewarding.

[Frosty]

That looks pretty tight for two Yanmar 6LP's.

There is a big intercooler on the port side and a big turbo on the Stbd.

Twins are better but you need a tape measure.

Yanmar 6Lp are good engine --high reving for a surface drive but then again your engine room is tight in so much as length with a gearbox.

If you wait a couple of days I can give you all dimensions of the Yanmars ,--I have a pair.

[Submarine Tom]

Piperca,

I don't envy your dicision position.

Pull out a piece of paper and list the pro's and con's on each side and then

give them an importance value of 1-10. This may help give you a

numerical summary of your desires.

Have you considered outboards? Like you need another option...

How important is weight to you?

What would you do with the extra bilge space?

Some other considerations may be:

resale value, ride comfort and noise level, stability (sea worthiness),

length overall, cost (install and maintenance), time out of service,

what the wife wants, and probably several other things I can't think of right

now.

Good luck! Let us know what you decide.

Tom

[daiquiri]

Just one shallow question - why do you want to switch to diesels? Diesel engines are an excellent choice if you spend a considerable amount of time at sea. In that case the overall fuel cost savings can compensate for the bigger cost of diesel engines in, say, 4-5 yrs of use. So the first thing to do is an estimate of number of engine operating hours each year.
In case you already did this math and decided that diesels are the way to go, than you have to take care of several things over there:
- weight of new engines vs. the old ones. You have a planing boat over there and the weight distribution is an important point.
- dimension of new engines vs. available space.
- don't forget to leave enough space for a mechanic to visualy control and insert his hands between the engines and do whatever he needs to do. You shouldn't leave less than 30 cm (12") of spacing.
P.S. - no, surface drives are not what you need if you are looking for good low-speed and trolling capabilities.

[piperca]

I weighed the gas/diesel dilemma and this is what I found:

-Gas is about 7k a side (Marine Power w/closed cooling).

-A couple of low hour diesels would cost me about the same and I could use my existing drives (280s).

-A single Yanmar is around 12K; outdrive, another 5K.

-I installed new fuel tanks, which have never seen fuel.

-No GAS under my aft berth to blow up my wife and kids.

I've got one BRAND NEW Volvo Penta 31P-A (4 cylinder, 150hp), but haven't been able to find a match ... this would be the easiest option. I'd snug these up to my existing Volvo Penta 280s and call it done!

The Yanmar would reduce weight, reduce overall maintenance (single vs twins), reduce fuel burn, but I'd sacrifice maneuverability. I would probably see better performance from the Yanmar than the twin Volvos, due to the drop in weight and higher horsepower rating of the Yanmar. I'd need to invest in a newer outdrive (Bravo 3x or equivalent), which will set me back a few more dollars.

So, I think I've settled the gas versus diesel dilemma regarding the difference in cost to repower; therefore, I can shelf that.

Now, back to the original question; twins or single?

The Volvos are no bigger than a gas 350, so I know I'll have plenty of room after installation. In fact, I've seen a lot of Skipjacks with twin Volvo 41s installed (6 cylinder), which is the choice setup for this boat, so I'm not concerned.

I guess maintenance and maneuverability appear to be the main issues, which gives a knock to each category, single and twins ... which can I live with???

Thoughts? Am I missing anything?

[Submarine Tom]

"Now, back to the original question, twins or diesel."

Diesel.

[piperca]

"Now, back to the original question, twins or diesel."

Diesel.

Got me! :p

[Jango]

Been following the discusion and based on what I've heard, I would go for Twin 150HP diesels.

[mydauphin]

If you are going to keep boat....Diesels, Make sure you use closed cooling and route exhaust properly to prevent salt water flowing back into engine.

[piperca]

Been following the discusion and based on what I've heard, I would go for Twin 150HP diesels.

That's the way I've been leaning, but the nearest rebuilt I can find to complement the new one is in Vancouver, Canada! I guess I'll just be patient and see what turns up. I've got another month or so before the house remodel is complete.

[big-boss]

What did you end up with? I am in the same deliema but with a 27ft Uniflite and I have two ASD-6 Surface drives.

[piperca]

I'm leaning towards the twin Volvo four bangers, but I've got to find a second engine that will meet my needs. I think I'll be sticking with Volvo 280 drives, since all I've read regarding surface drives does not fit my application (fishing, trolling, etc.).

[piperca]

Okay, I may have found that second engine to complete the twins setup ... yeah!

Minor problem: My existing drives are VP 280s with a V8 gear ratio (1.61:1, not sure). Anyway, does anyone know what ratio I should be running? If I were to stick with the existing drives, what issues would I have?

Thanks in advance!

[Karl2]

Piperca,

1.61:1 is the ratio to run with the 280 drive. The 150 hp 31 was never offered on the 280/290 style single prop drive. The last version was predominantly sold with the Duoprop drive and then with a 2.3:1 ratio (Don't compare ratios between duoprop and single prop drives). The engine was offered with the "SX" single prop drive (The drive used on Volvos gas motors) and then with a 1.79:1 ratio.

Looking at it strictly from an effiency standpoint you would be better off with a 1.8 - 1.9:1 ratio but you would then sacrifice gear life - Don't go there.
If you are looking for efficiency (And several other performance related benifits) spend your money on Duoprop lower units, look for used ones with the 1.95:1 ratio (The 2.3:1 ratio requires a complete drive - this ratio is made up with a reduction in both the lower and upper gear case). Or, if you have the apetite and the $; I believe Volvo has an exchange program were you give them your single prop lowers and they will sell you duoprop lowers.

Again, If you stay with the 280 units stick with the 1.61:1

Good luck

Karl2

[piperca]

Thanks, Karl2!

One of the engines I will be using is new and has attached a HS1 gear in the 2.62:1 ratio; that made me think I was way out of sync. Obviously, there is a bit of a difference in ratios; what is the greatest difference I would see between the two?

[Karl2]

I'm not sure I understand your concern. Both engines will be coupled to a 280 drive with a 1.61 ratio. The HS1 gear with the 2.62 ratio will be in your garage or sold off to someone.

Karl2

[piperca]

I'm not sure I understand your concern. Both engines will be coupled to a 280 drive with a 1.61 ratio. The HS1 gear with the 2.62 ratio will be in your garage or sold off to someone.

What I meant is what performance related issues would be seen running the lower 1.61:1 gear ratio in comparison to a higher gear ratio, as in the ratio of the gear that accompanied the engine. Obviously, that gear ratio was coupled with that engine for a reason or am I missing something? Sorry, I'm a complete amature in regards to this topic. :o

[Karl2]

OK - Understand.

When I say that perhaps a more ideal ratio (from an efficiency standpoint) would be a 1.8 - 1.9:1 I speculate that such a ratio would be a better match for the speed range that this engine/boat combination will result in. A 1.8 - 1.9 ratio could result in a small top speed increase and probarbly better acceleration. This would be small differences and nothing you should loose any sleep over.

The 2.6:1 gear that the engine came with is a bit unusual. Most of these motors in the in-board configuration were sold with a 2.0:1 gear. The 2.6 was probarbly destined for a bigger/heavier/slower boat were you need to swing a bigger diameter prop to get decent efficiency.

Again, in your case you will be just fine with the 1.61:1.

Karl2

[piperca]

Excellent, Karl2, I really appreciate your input!

One last question, if you don't mind. What would you recommend as a starting prop size in this configuration? The boat is a 28' Skipjack Flybridge, which has a dry weight with engines of approximately 6600lbs. I am hoping to gain a speed of around 18 knots cruise. The prior setup (twin AQ225Ds, 225hp 305s) I was getting around 16 knots cruise; I was running 15x17s. I have a pair of 15x19, but I feel they might be a bit under sized ... what do you think?

[Karl2]

What was your top speed with the 225's and at what rpm ?

Karl2

[piperca]

What was your top speed with the 225's and at what rpm ?

Karl2

I don't really know what my top speed was, since I never had any reason to run her that hard. The cruise was 15-16 knots (18-19 mph) @ 3100-3200 rpm. WOT on that engine is 4400. I had her at 4200 once (momentarily), to check that the engine was propped correctly. I didn't want to max her out in the sea conditions at the time and was happy with the 4200, since I still had a little throttle left ... that was running 15x17s. I failed to check the speed at that time ... stupid Andrew!

[Jango]

According to Prop Calc your props should be 17 x 16,s. Larger props are requires due to the slower running motors - 3600 RPM Max. w.1.61 gears. Top speed at 7600 lb disp. should be around 24 knots, with a cruise of 15 knots @ 2500 RPM.

[Karl2]

OK – I’m going to guess that the boat is a bit heavier than 7,600. My best estimate is a top speed around 24-25 knots. Prop should be selected so you can get 3,900 @ WOT (These engines are NOT 3,600 rpm) with a loaded boat. If you achieve 24 knots at 3,900 rpm you can, safely, cruise all day @ 3,400 – 3,500 @ 20+ knots. So..Given that the above pans out your 18 knot cruise target should be there and at a very fuel efficient rpm.

As to the prop: Jango is correct – This combination (Engine hp and rpm/gear ratio/boat/speed range) would work better with a larger diameter wheel. However 17” is not available and would not fit.
Volvo has 16” diameter props. My calculation falls right between a 16x15 and a 16x17. My recommendation = 16x15.

Karl2

[piperca]

Thanks Jango/Karl2!

Okay, another problem just arose; the engine I was looking at turns out to be an AD31B and not a match to the 31P-A that I have. The 31B is a 130hp engine and the P-A is a 150. Is it possible to tune the 31B to match the performance of the 31P-A for a twins setup? I am having a terrible time trying to track down another P-A!

[piperca]

Karl2, I calculated out, approximately, what the boat would weigh fully loaded.

I figured 6600lbs dry, 1200lbs fuel, 800lbs for 4 persons, 500lbs gear, 600lbs bait tank and fresh water tank. Looks like she's running not a kick in the butt off 10,000lbs. Would this affect the calculation for the props?

Of course, when I'm out with the family on a cruise, she'll be close to 1000lbs lighter, since I probably will not be fishing.

[Jango]

Very little effect on Props - Calculates to 16x14 Props @ 3900 motor rpm with 1.6 gear, 9000# total, resulting in 24 Knots w. 15% slip. Cruise should be at least 14 - 15 knots @ 2600 rpm ( abt. 24% slip)

(You may get by with 16x15,s but 16x14,s are ideal with 300 max HP and the heavier load)

[piperca]

Very little effect on Props - Calculates to 16x14 Props @ 3900 motor rpm with 1.6 gear, 9000# total, resulting in 24 Knots w. 15% slip. Cruise should be at least 14 - 15 knots @ 2600 rpm ( abt. 24% slip)

(You may get by with 16x15,s but 16x14,s are ideal with 300 max HP and the heavier load)

10-4, thanks for the info!

[Jango]

With 130hp engines, props would change to 15.5 x 13p. Max top speed of 22 knots @ 3900rpm w. 9000lb total. 16% prop slip. Ideal Cruise speed could be slightly less, depending on rpm

[piperca]

Well, guys, you've been more than kind with your responses ... thanks!

Now I'm going to throw a wrench in the plan ... I've changed the engine!

I'm looking at a pair of Yanmar 4LHA-STEs (230hp each). Do you think that these engines will be too much for my boat (28'Skipjack Flybridge (http://skipjack-boats.com/history_28fb.html)) and/or my Volvo 280 outdrives? I don't want to waste my time, or the the sellers time, if they are too much for my applications ... what do you think?

[piperca]

Okay, I did some research and, in my mechanic's opinion, the drives will be fine; however, he doesn't like Yanmars ... he's a Volvo guy! Well, tough, it's not his boat!

As far as hooking up the Yanmars to the Volvo drives, this is what I came up with ... please, someone correct me if I'm wrong!

To mate the Volvo drive to the Yanmar, I'll need a flywheel cover with a Borg Warner bolt pattern and an old Volvo AQ190 or AQ240 bell housing. I'm led to believe that, since these engines were Fords, these bell housings will have the same bolt pattern as a Borg Warner gear, which will complete the puzzle from the engine to drive ... is this correct?

Is there a flywheel cover that will fit the Yanmar that has a GM bolt pattern, so that I can use the bell housings off my old AQ225Ds?

Another dilemma ... the exhaust! Is there a fitting that'll accomodate the exhaust gasses (something similar to the old Y pipe) or do I have to cut the exhaust through the transom?

Thanks in advance!

[mohamed atia]

after following all ur comments i think:

if you dont spend more money twin will be good at first installation but be a ware about running cost for your working hours.
and yanmar one will be as spend money at first and save in running cost after that.

finally i thing the two ways r the same the decision is yours only

thx for your time

[piperca]

Well, after much research and thought, I am about to pull the pin on the repower. It will take me the best part of the year to put it together, but I've got plenty of time.

I have decided on the single Yanmar diesel ... a 6LY or LP, reconditioned, which should take care of the early valve dropping issue. I have found a company that will do the transom fiberglass work for me, which will not cost an arm and a leg. They are a reputable company and fiberglass is their forte.

I have figured that, if I do it right, I should be able to get her done for around $30k ... that's why I'm taking my time and piecing it together over time. As the project matures, I'll post a pic or two and keep you up to date ... I think it will be interesting for some to follow.

[Brian@BNE]

I first opened the thread today. IMHO a single diesel was a standout solution at the outset, but I enjoyed the read. Should end up a much improved boat. And your drive will be?

[piperca]

I'm leaning towards the Volvo DP drive, but have not excluded the possibility of a Bravo 3. I'm still researching the options.

I have a friend that is running a 6LP in a 27' Grady Sailfish with a Volvo DP drive and he loves it ... zero problems after about 5 years of heavy use. His boat is heavier than mine (dry weight) and has a full tower with second station ... plus it's a 9-1/2' beam. He tops out at around 28 knots and cruises all day at 23-24 knots. My boat is an 8' beam and the only modification from the originally rated dry weight is a half tower. I should see better numbers than he is seeing ... hopefully!

[Reelalure]

Your already set up go with the twins save a bunch of problems and time. Twins..... I just went through the gas or diesel but with a single engine,I decided on cummins 6bta 370hp. This also depends on how long you plan on keeping the boat, resale value???? is it going to matter in the hull you are useing. Look up similiar boat with gas and diesel and see what the resale difference would be. diesel is safe, dependable. I am also not a big fan of volvo diesel. But if you are not going far from where you can get expensive parts it is not a problem. Good luck, Ken

[piperca]

Ken, I'm not concerned about the resale value, as I don't intend on selling the boat any time soon. If anything, I'll probably end up giving it to my son. The hull is sound and the boat has an excellent reputation here on the west coast, so I don't mind investing a few dollars in the propulsion system.

I'm looking for something that is reliable and economical, neither of which is gas or twins. The safety factor is huge, also, so a single diesel is probably the way to go for me.

[Easy Rider]

If the safety factor (i assume tour'e talking about redundancy) is even above average I'd say twins is the way to go. But basically I think if you can afford it twins are better. Twins get a demerit if you boat where there is a lot of floatsam in the water but before commenting any further I better read the previous posts.

Easy Rider

[fg1inc]

One more thing to keep in mind - vibration! Two four bangers in that little boat will shake it apart and no special mounts will fix it. My vote would be single Yanmar.

[Stumble]

Personally for any offshore work I demand two engines. I have been caught out enough times when one craps out that the safety factor of a second means of propulsion is worth it to me. But if you are set on going with a single, then I would highly recommend an outboard kicker, with enough fuel to get you home, just in case.

[u4ea32]

I think the single six cylinder Yanmar diesel is the way to go. IMHO!

I've run tens of thousands of miles in single diesel boats and never had a problem that would have been better with twins. Sure, sometimes one needs to mess with filters, but fuel is the single point failure on twins -- if a single dies due to clogged filters, both engines in a twin would also die. A lightly loaded diesel, like a single 315 in a 10K boat going 18 knots, will be tough.

In fact, my own boat, also narrow beam (8.3 feet wide) with twin gas (in my case, twin big blocks) is going to need a re-power: both engines have failed. My boat weighs the same as yours. While my boat could top out at 70, in fact I also cruised around at about 22, as that's how fast the Pacific allows small boats to go!

So I'm in the same place as you, a year later.

My options:

1) Just sell it now as a project boat: as-is.

2) Get rebuilt engines and just sell the boat. I really am fed up with twin gas, so I would not want to keep her with twin gas I/O engines.

3) Put small twin diesels in there. But as you have discovered, that's expensive. And still twin engine maintenance, and lousy service access.

4) Fill in the transom holes, and change the stringers, and put in a single diesel, like a yanmar six as you've selected.

As with your boat, I think only the single diesel option makes sense of the above.

However, one more:

5) Twin outboards! Twin Optimax 150 or 200s will work for Pacific Ocean speeds.

The outboard option, like the single diesel option, requires some fiberglass work to the transom. But the outboards would allow all the structural stuff inside the hull to remain the same, so that should be cheaper. On a Skipjack 28 you've already got a flat cockpit floor, but in my boat, this would make my cockpit big and flat. Nice! But of course, some expense for the new cockpit sole.

Installing outboards is MUCH MUCH easier than any I/O or inboard, and certified pre-owned can be less than $10K each, perhaps much less.

And the huge weight savings -- 2500 lbs less weight, and the weight further aft which is better for a planing boat -- should really help fuel economy. And from what people say, these "orbital charge" Optimax are more fuel efficient than EFI 4 cycle engines. Light+efficient might make a noticeable dent in my fuel bill.

For those of you not from Southern California: around here, its pretty typical to run 100 miles, and not unusual to run 200 miles in a weekend. On four day weekends I usually run about 500 miles. The islands are out there, they are big, and the interesting cruising places and good fishing places are way the hell out there.

Hopefully my wife won't read this, but we run an average of 200 hours per year, and have been burning 20 gallons per hour at our Pacific cruising speed of 22 knots, so that's 4000 gallons per year at $3.50 or $14000 per year. And if I had to buy fuel at a gas dock instead of gas station on land, then the fuel cost would be $20K per year! So in California, the cost of fuel really has become the biggest cost of ownership, by a good margin.

[capt littlelegs]

Twin engines means you have twin main or day tanks and change over filters for each engine so twin diesels are four times more reliable than one diesel with only one filter and diesel is far more reliable and economical than gas. Normal service maintenance shouldn't be anymore difficult with twins. Outboards are expensive to buy and maintain with a much shorter life.

[apex1]

Twin engines means you have twin main or day tanks and change over filters for each engine so twin diesels are four times more reliable than one diesel with only one filter .... Normal service maintenance shouldn't be anymore difficult with twins.


What a utter nonsense. How can twin engines be 4 times more reliable? Who is mad enough to have only one filter on a single engine?

Are all the fishermen, is all the commercial shipping world just mad to choose only one engine for propulsion?

[FAST FRED]

one engine for propulsion?
__________________

Really big difference between an industrial engine and a marinised car take out.

FF

[Easy Rider]

I remember real marine engines. There aren't any anymore. They had flywheels on the fwd end, updraft carbs and some had cast iron oil pans that were common to engine and gearbox. Lathrop, Hercules, Red Wing, Palmer, Chrysler, Gray, Nordberg, Kermath, even Owens and Chris + Craft. One of the best engines of the 50s still exists today ..Universal.
Where do they get 350 GM engines? Must be car engines. Never heard of a 350 Chev industrial engine. Diesel marine engines basically all come from industrial stock ..is that not true Fred?
Oh .. about the question. Twins are better. Like most things better ..more expensive.

Easy Rider

[FAST FRED]

Never heard of a 350 Chev industrial engine. Diesel marine engines basically all come from industrial stock ..is that not true Fred?

The Chebbies come from a long supply line , both truck stuff (salt cooled valves) and racing stuff Forged crankshaft is off the shelf and cheap.The camshaft of your choice and the matching intake will put the HP at whatever rpm you desire.

Crusaider does a good parts selection , would be worth researching and copying , or just by a Crusaider.

In the more modest 250 to 500 Hp range most boat diesels are either from earth moving machines , ( CAT or John Deere ).

Many will come from the generator or trucking industry , Detroit .Cummins.

Dedicated marine engines are only in really large sizes as the 4000+hp EMd is actually a train engine .

Once the cruise rpm is about 100rpm , its a modern marine engine.

FF

[apex1]

Diesel marine engines basically all come from industrial stock ..is that not true Fred?
Easy Rider

No that is not true, at least not for all brands. It would be as valid in several cases to say the industrial engines are derived from marine engines. Some Deutz, MAN, MTU, Detroit for example.

There are still some of the "good old" diesels around, though not the brands you named, but Bukh and Sabb are alive.

Have no comment on the chevy´s, because the questoin was single or twin DIESEL.

Regards
Richard

[girvin]

just please don't get the vovlo penta. They have alot of problems like impeller shafts shatter time and time again. We have gone through 3 engines, one of which only got 1800 hours. I am trying to get my boss to change on the next go around.

[girvin]

Ohh and go single with a outboard kicker and its own gas tank. Its a good proven combination that the west coast whale watchers use and for use its all about being able to be safe in some serious waters and still make the best profit we can. We put about 40 - 50 hours a week on each boat for 4-6 months a year.

[mark775]

I have tried to stay out of this because I already weighed in and I thot the thread would atrophy soon but "please don't get the vovlo penta" ? made me come back. Any engine one finds will have opinions "Yea" and "Nay". More than what color the engine is, the quality of service shud be one's deciding factor, IMO. I have a Volvo I trust my life to but that is not why I'm writing - It could be a Cummins or Scania or several others, I could sort out its idiosyncracies and be happy for decades. With a diesel engine, run slow to run long. Getting a load on the engine is critical but too much of a load is worse than too little. If the boat is not to have CP, prop it so that it gets all of its rated RPM +, FULLY LOADED, back off at least to the recommended cruise RPM, find a "sweet spot" and watch your pyrometer and boost gauge for changes from the norm. Change your oil often, have a temperature sensor installed on your exhaust mixing elbow, change zincs on schedule, have the thing perfectly aligned, lots of dry air to the engine space, a shaft with a safety factor of at least five, feed it CLEAN, DRY FUEL and have a healthy electrical system. If one does these things, he will find satisfaction in his boat and almost never lose independence. In today's world, wonder why big "battlewagons" sell for so little relative to new? Why there are NO big Bertrams under construction at this time? Because unless there is a SPECIFIC AND QUANTIFIABLE NEED, twin engine boats are so much more expensive, LESS reliable than a well loved single, and less economical that they are an anachronism. Get one cheap and live aboard. To go to sea, get a single engine boat.
Notice, too, that the most experienced mariners agree. Tho consensus does not make right, it's a damn fine place to start.
None of this advice applies if one is the type to run it hard and put it away wet - for those, two, three, four engines are more appropriate. In fact, if in that catagory, I have to question a person going to sea at all under his own responsibility. Just charter a good boat and allow a pro to take care.

[girvin]

I don't mean to bag on volvo maybe just the 330 and 310 I have thousands of hours in them and just think there are better alternative. THe bigger volvos I thinks are better. WE ran ours at 2700 rpm to 2800 never ran more than that and we have excelent mechanics and never missed a service. Just my experience, not law. Not trying to say they are all bad but every charte company here has had issues. 7 boats running them total. I am still a single engine kinda guy though.

[mark775]

Out of curiosity, what is the model that has problems and what are the specific problems? I think this applies to the intent of the thread...

[girvin]

the 310 and 330 have impeller shafts that shatter and the engine overheats and burns up. It has happened to every boat here running this engine at least once and we all have impeccable maintenance. we only got 1800 hours out of our last one and the guys next to use got 4000. Volvo says they will last 5,000 I have yet to see one get there out here. We don't have a choice though only one mechanic shop in town and 8 tour companies with alot of boats.

[mark775]

I am not familiar with those models. Are they similar to the 40 series or D6?

[girvin]

No I think they are different. they are the high horse higher revving ones used in planing hulls ours is in a 31 ft aluminum covered boat.

[mark775]

Our local Volvo guy is genius - I'll see if he has an answer...

[piperca]

Wow, I'm surprised how much traffic this thread has got since my last visit!

As before, I have been wavering back and forth, but have stumbled across a pair of Volvo Penta 41Bs that may be for sale very shortly. They have about 300 hours on them, so they might just fit the bill.

The mechanic I am using is a certified Volvo Penta guy and has been around this area for years. He swears by these engines and thinks it would be a wise choice, given he's seen a lot of these engines in this specific make boat and feels they give excellent performance/fuel economy.

Based on this configuration, what would be the best prop selection?

Twin 41Bs (200hp); 280 outdrives (1.61:1, single prop); boat weight approximately 10,000lbs, loaded. (That's 7,000lbs dry weight, 1,500lbs fuel/water, 1,500lbs gear and persons)

What kind of cruise, etc, would I see from this setup?

Also, I have replaced the original tank (140 gallons) with two 82 gallon tanks. I am considerning running the engines off individual tanks. Do I need a separate vent for each tank? When grounding the tanks, can I run the tanks in series or do they need individual grounds? I am using Racor 500MA filters; should a 10 micron element be sufficient at the tank? Any additional input on this subject would be appreciated!

[BTPost]

For best Design, you should plumb both tanks to feed a separate Fuel Header for each engine, so that if you contaminate one tank, you can still operate on two engines from the other. In commercial vessels, they sometime plumb an Emergency Tank (50USG) into the Return Lines, that then overflows back to the Main Tank. This gives you 50USG, of CLEAN Fuel, that has been thru your Filter System, Injector Pumps, and Injectors, and is KNOWN Good Fuel, that then can be switched into the Engine Fuel Header, should you take any Contaminates into your Main Tanks. Leaves you 50USG to get home on, when ALL Else Fails. 10 micon Racor's will do you fine, for Main Fuel Filters. Just make sure you have two more than you ever figure you will ever need, aboard, at ALL Times, plus a couple of sets of whatever you are using a Secondary Fuel Filters. The old saying,that covers Fuel Systems is: A Prudent Skipper, NEVER runs out of Fuel Filters, NEVER... A little extra piping, NOW, will save you hours of misery, down the road.

[piperca]

I saw the description of that fuel system layout in another thread. One problem I see with my setup is that I do not have room for another 50 gallon tank, or any tank, for that matter. I had thought about running both engines off one tank at a time, but my mechanic brought to my attention the issue of rotating fuel supplies. There is a higher possibility that I'd run the same tank each time I'm out, which might cause fuel problems in the other tank. The other thing he mentioned was separating fuel, air and power to each engine, so, if I did have an issue with one engine, I would always have an engine to get home on ... that made a lot of sense to me.

The Racors would be mounted directly off the tank and would filter the fuel before the engine-mounted filter unit. I think this would be sufficient filtering, don't you? I did think about doing a double 500MA system, but I think that's a bit overkill.

[mark775]

There are some fine points with BT's post that I disagree with but will work fine.
I'd probably just cross the tanks over. I'd also like to see a larger capacity Racor and if you are going to replace anyway, a system like mine is cleaner and has far more capacity.

44021

Mind you this for a single engine.

[piperca]

That is a pretty clean setup!

The Racor 500MA allows for 60GPH, which I think is plenty for the 41B. That coupled with the engine mounted unit seems plenty, don't you think? I don't know what size Volvo engine you're running, but, by the look of your engine room, I'm sure it is much bigger than a 41B. Wish I had such a space available.

What do you mean by "cross the tanks over?"

[mark775]

Well, I think that the 41 burns something like 10GPH and flows almost that back to the tank. Multiply that by two and you are looking at 35GPH total flow running thru a filter with 60 GPH flow potential if completely clean. It will work if everything is just so until you replace with common rail engines which flow much higher.
By cross over I mean connect the tanks so that the fuel levels. It works well this way. I wouldn't use copper lines even tho I did - I just did it because it was always that way and copper was cheap...once. My preferred fuel lines are Swageloks and stainless tubing with a short fire resistant fuel hose to the engine.
My thots on engine space are that the more pleasant the space is, the more likely you'll want to stay there and do maintenance. The bigger Volvos have a shelf that catches oil when changing filters. That and the plumbed in oil change pump make it a half-hour job on my boat to change oil. Filters almost never need changing as the first one is high capacity "trash" filter, the second, ten micron, the on-engine filter, two, I believe. Only change out a filter when the drag pointer changes position (mine hasn't in three years), drain a bit from the filters each day to see if there is water.

[piperca]

I think maybe I should explain my setup ... I think I did earlier in the thread, but here goes.

I have a small 28' sportfisher (http://www.skipjack-boats.com/history_28fb.html) , which has an 8' beam. The original engines were twin VP AQ225Ds (Chevy 305s) attached to VP 280 outdrives. The original fuel tank was 140 gallons.

I removed the original tank and replaced it with two 82 gallon tanks, one forward of the other, installed along the keel line, forward of the engines. Here's a photo of the bilge area where the engines sit:

http://i275.photobucket.com/albums/jj316/piperca/P4060004.jpg?t=1275840269

Here is the area where the old tank was removed:

http://i275.photobucket.com/albums/jj316/piperca/Boat/P4060003.jpg?t=1275840558

Here are the new tanks in place:

http://i275.photobucket.com/albums/jj316/piperca/Boat/P4130046.jpg?t=1275840647

This will at least give you an idea of what I'm working with. I think, to keep the fuel level, I would need to run individual tanks to each engine, correct?

Also, does anyone have input on the prop size I asked about a couple of posts ago?

[mark775]

Hey, Piperca. I'm sorry, I made an assumption that the tanks were athwarts. Two observations; First, ideally there is air circulating around that tank and it never sits in water. Can you get it up even an inch higher or does this compartment stay completely dry? Second, if there is ever any moisture in that compartment, even condensation, it is not good to have brass in contact with aluminum - the AL is more noble and will rot from electrolosis. I have stainless bushings between my brass and aluminum and it is still the first area to rot on my tanks, albeit it took 31 years and still doesn't leak.
I think the twin 41 Volvo setup is a good one, BTW. My preference is always for a single so that there can be a nicer space but you are almost already there with the twins. I don't know these engines but they are the ones all the little charter boats here seek - they are considered more reliable than later ones.

[piperca]

Yes, the tanks will be raised to allow air to circulate, I just haven't got around to permanently securing the tanks yet. This area does stay dry all of the time and has excellent ventilation.

The old tank was of the same construction as the new, in fact they were made by the same company. The old tank was 30 years old and did not show any signs of corrosion around the brass to aluminum union. All of the Skipjacks had the same tank manufacturer and still do. He's been supplying the pickups and immediate fittings for all of these tanks, which are copper pickups with a brass elbow. To tell you the truth, I have never seen any condensation in the bilge of my boat, so maybe this is the reason there isn't any corrosion.

[mark775]

Great. Keep up the good work and post pics as you go!

[piperca]

Maybe someone would like to give me a suggestion on how to accomplish the following.

Take a look at this picture and you'll see the bottom of the tank doesn't quite fit the contour of the bottom of the boat.

http://i275.photobucket.com/albums/jj316/piperca/Boat/P4130044.jpg?t=1275875030

I would like to shim the underside of the tank, so it has support. I tried using Starboard blocks, adhered using 5200, as in this photograph:

http://i275.photobucket.com/albums/jj316/piperca/Boat/P4120040-Copy.jpg?t=1275875213

However, the 5200 did not stick to the aluminum. I was thinking about using Alumiprep 33 and Alodine, then painting the bottom of the tank where the shims would be placed. After painting, I would drill several holes or cut grooves in the Starboard blocks then use 5200 to adhere them. The holes or grooves would provide an area for the 5200 to accumulate to hold the Starboard shims in place ... do you think this would work? Does anyone have a better idea.

I thought of placing a couple of wooden shims along the length of the tank, but attach them to to hull. Glue a rubber strip on top of the shim and then a bead of 5200 between the rubber and the tank ... am I getting closer ... LOL!

Any suggestions would be greatly appreciated!

[mark775]

I know you are sick of paying a welder but I would have angle welded on the sides and simply hang them from the stringers. It will be more than strong enuf and there will be no point of water contact.

[piperca]

Do you honestly think that the angle bracket would be strong enough? There would be about 660lbs of fuel in the tank sloshing around. I had thought of that but decided I was asking too much from an angle bracket. I guess I could put something under the tank at the keel and then have brackets on top of the stringers on either side ... what do you think?

[mark775]

Yes, the angle will be strong enuf - just use 1/4" four by four angle on the thwarts of the tank (or go full length). They will stiffen it and it's not going anywhere (I see you were cautious on the fore and aft baffles so I will assume that there is one running the other way, too). I have a twenty gallon tank for my Espar hanging by three 1.5" tabs of 1/4" angle. It doesn't even wiggle. Granted, 82 gallons is a long way from twenty but I have seen this done many times and consider it preferred to any other method. Even in a wet environment, the SS lagbolts can be moved over a few inches when they rot the aluminum out after 15 years.
Just out of curiosity, you said you used 5200 on the Starboard but it looks like silicone - you must have used denatured alcohol to neaten it up - how did you know to do that?

[piperca]

I actually used acetone.

I cleaned the tanks with the acetone, then applied a coat of 5200 to the underside of the Starboard block and affixed it to the tank. Once the the 5200 squeezed out the sides of the block, I removed as much as I could by mechanical means, then used an acetone soaked cloth to clean and tidy the 5200.

[Reelalure]

piperca, When i put new tanks in a boat i like to foam them in to support them. For drainage run lengths of pvc pipe under tanks fore and aft, Hang the tanks temperaraly with some pvc straps. Build temperary bulkheads from cardboard or luan fore and aft ends to keep foam contained around tanks. Or you could build a permenant bulkhead on aft side of tank witch would help support the tank from move aft and then use that bulkhead to mount your filters on or anythingelse you may need to mount. Keep your drain pipes out the ends, Use coast guard approved 2-part foam found at Boat fiberglass supply shop it comes in a few densities or pound weight i use 4-lb on mine any lighter will crush over time. even adds some floatation, stiffness, vibration and sound deadening to the boat. Do not use lighter floatation foam for tank setting. you want the stuctural 4 lb or more. If you are concerned of ever removing or moisture you can rap tanks in plastic or viscuine before you pour. This is a closed cell foam i am refering to. when you remove the temp. bulkheads you can glass or epoxy around your drain pipes if you feel it is needed to make more water tight. When the foam is hard you can form it to any shape with knives and sander, Just depends on how fancy you want to get. This is common practice in a lot of boats. You do not want your tanks rubbing the inside of your hull. Bad news there. The foam will support the whole tank bottoms and sides up to the top of your stringers. Are your tanks mounted forward of midships? they will take a beating. And they are large heavy hammers pounding on your boat. if you plan on planning this boat at a cruise speed.This is one reason most planning boats have tanks mounted midships or aft.There are several different way's of doing this. This is just one way to foam tanks. PVC pipe is easy and cheap way, you can take fiberglass pipe cut in half and glass to the boat under tanks then glass ends to permenant bulkheads. just depends on how fancy you want to get. $$ Good luck. Ken

[mark775]

No...

[gruenemachine]

Have u ever looked at an engine mfg called Steyr ,,, high revolution diesel with small footprint and weight to power ratios are awesome... Many people are switching from mercruisers gas to this diesel with great performance success and not a total retrofit to install... just food for thought

[piperca]

Ken, I have considered foaming the tanks and my mechanic thinks I am a fool to not do it, since the area the tanks are housed is always dry. He thinks that corrosion would occur after another 30 years, if at all! If I am to do the foam method, I will run drainage under the tank.

Gruenemachine, yes I've heard of Steyr, but I am not considering them at this time. Funds and application are both issues, but thanks for the information.

Mark, what do you mean by "No..."? Foam?

[mark775]

Just my opinion. I have seen a lot of damage due to this. I can see an application - boats that are thrashed hard and you want the tank and foam to be part of the structure but my life is centered around making things last for the long haul and if any moisture gets in there, EVER, the whole mess turns to mush. I just don't see a reason to do it other than it is easy and looks very stout until it comes apart and the tank leaks into the foam.

[apex1]

Just my opinion. I have seen a lot of damage due to this. I can see an application - boats that are thrashed hard and you want the tank and foam to be part of the structure but my life is centered around making things last for the long haul and if any moisture gets in there, EVER, the whole mess turns to mush. I just don't see a reason to do it other than it is easy and looks very stout until it comes apart and the tank leaks into the foam.

Concur Mark.

No foam under tanks! The "dry areas" are not always as dry as we like them. And proper access is one of the "secrets" of your boats bristol shape.

Regards
Richard

[piperca]

Okay, I've heard this time again and I understand where some might be coming from; however, I am considering using foam. The original tank had 30 years of use and the only reason I replaced it was due to it probably being time. The tank didn't show any signs of corrosion.

The way I am intending on using the foam is on the sides and partially across the bottom. IF water was to get under the foam, it would be able to escape at the underside of the tank. As I mentioned before, I am also considering painting the area that will be foamed. What do you think? I will try to post a drawing of what I am considering.

Update: Here is what I am considering ... comments, please!

http://i275.photobucket.com/albums/jj316/piperca/Boat/Tank.jpg?t=1276145045

The yellow being the foam, black the boat and grey the tank.

[apex1]

Perfect moisture trap, congratulations! That is exactly the way the industry does it (or did at least) in mass products, where nobody asks for service life.

Listen to Marks comments, he knows from (painful) first hand experience what serves him well.

Regards
Richard

[piperca]

Thanks for the sarcasm, it was helpful!

If you look, the foam is only along the sides and part of the underside of the tank. The area of the keel and a portion of the underside is free of any foam (white area on drawing).

I was offering this for constructive criticism, since I thought leaving the underside free of foam would eliminate the chance of moisture entrapment. Also, as I mentioned in a prior post, I was going to treat the underside and sides of the tank with Alumiprep 33 and Alodine, finishing it off with an epoxy paint. Surely this would eliminate the possibility of corrosion.

I have spoken to the tank manufacturer and a few local marine shops and they all concur that hanging the tanks from the stringers without additional support is a bad idea. The possibility of the tank twisting and weakening the welds is their main concern; therefore, I need to find some way to support the tanks from below. Does anyone have any ideas?

[mark775]

Do what you were going to do anyway.

[piperca]

Mark, I understand the issue with foam, but I am trying to come to some compromise here. I am throwing out these thoughts and ideas for feedback, not because I am set in my ways and am going to do what I intended, anyway.

If you would like to comment on what I proposed and provide me reasons that certain things might be an issue, I think that would be very helpful.

Update: I did some surfing and read a very interesting post on another site. Here is part of a response that hits on what my concerns are ... and the concerns of some of the people I have spoken to ... good read!

"I’m still stuck on the material fatigue issue. Devil’s advocate here, I’d make the remark that I’d rather have a ¼” thick tank wall, foamed in, with an effective epoxy barrier coat, and try and manage the failure mode of corrosion, then to try and intermittently support an aluminum tank with the risk (however low) of catastrophic fatigue failure. When you mount an aluminum tank what is the fatigue life in cycles? You have localized stress concentrations that may be above the endurance limit of the material. How do you know with unknown load conditions and unknown material properties (in the vicinity of the welds)?

Note that a corrosion failure will likely be a pinhole leak, and may (hopefully) get noticed by smell before you get 600 gallons of fuel in the bilge. Not so a fatigue failure, when it goes, it goes-all of it.

How many “conventionally” mounted aluminum tanks with perfect drainage, no standing water and no corrosion fail from fatigue? I don’t know. How many T-Tops fail in the same way? That I do know-a lot.

All the speculation and worst case scenario stuff aside, and moving past bias and preference, is there any engineering reason why a properly mounted thick wall tank, coated with a non-permeable epoxy based coating (like coal tar epoxy), foamed into place with no standing water allowed , would EVER fail? If so, what is that reason?"

[apex1]

Well,

when you really coat it with Ep (that would be one primer film and one thick film layer at least) and have some space between the foam sheets, as you describe it, that could work well.

Regards
Richard

[piperca]

Richard, that was might thought. My only concern is that I've never worked with the chemicals mentioned and believe there is a trick behind using them. I'm led to believe that improper application can lead to corrosion issues, so I am researching this to make sure I am not headed for disaster.

Has anyone worked with Alumiprep 33 and Alodine? What might be the complications of an improper application? What, if any, are the tricks to applying these chemicals?

[apex1]

Richard, that was might thought. My only concern is that I've never worked with the chemicals mentioned and believe there is a trick behind using them. I'm led to believe that improper application can lead to corrosion issues, so I am researching this to make sure I am not headed for disaster.

Has anyone worked with Alumiprep 33 and Alodine? What might be the complications of an improper application? What, if any, are the tricks to applying these chemicals?

When you follow the application rules / schemes, provided by the supplier / manufacturer, it is no black magic to get a perfect surface. Then again do as the coating mfg tells you in the application manual and tataaa.. it works.

Apply a double coat of primer before you build up the Ep tar or whatever coat you have in mind. A single coat primer is insufficient! (I apply three primer coats of 50µ)

The main prob with all these materials is, that the homebuilder (and some self proclaimed Professionals) try to cut corners and apply insufficient methods and / or materials to save some pennies.

Btw. Armaflex AF is the foam you should use, when you use foam!

Regards
Richard

[M-Sasha]

Single Diesel.

Sasha

[piperca]

Thank you, very informative!

While pondering, I did think of an alternative that might keep Mark happy (no foam, LOL).

If I were to make saddles/straps that are about 3-4 inches wide and made of 1/4" stock. The saddles/straps would follow the contour of the tank and attach to the top of the stringers using bolts ... something like this:

http://i275.photobucket.com/albums/jj316/piperca/Boat/Saddle.jpg?t=1276304378

I would line the saddles/straps with 1/4" starboard (blue area in drawing), dadoed out to 1/8", to overlay on the saddle/strap to isolate it from the tank. The tank would be suspended by the saddles/straps off the hull of the boat. Tabs made of angle, welded to the sides of the tank, would secure the tanks to the tops of the stringers. I was thinking 3 of these saddles/straps would be adequate along the length of the tank (36").

What do you think? Would the aluminum saddle/strap be strong enough to support approximately 700lbs (tank plus contents)?