Repower questions

Hi Chris,

Yesterday I had a big tree to fell without ruining the surrounding palms and my wife's pottery. Drained all my energy for 24 hours.

By now you have also read this: http://www.boatdesign.net/forums/diy-marinizing/marinizing-vw-turbodiesel-engines-19118.html so you must have some idea of what it in store for you if you go for VW diesels.

I think you first have to decide between normal prop shafts and external ones. With normal 15 degree shafts you have no problems to solve because all the required parts are off the shelve, but the engine location halfway the 23' hull takes up a lot of valuable living space.

External shafts allow you to move the engines to the stern, but again there are two options: surface piercing props or water filled tunnels.
Surface piercing is simpler but you have to accept more noise and vibration, also the props are unreasonably expensive.
Water filled tunnels are quiet and very efficient but involve more grp work. Now that you have read my thread a couple of times you will not make the mistake I made by designing the tunnels too short: they must start 1 ft forward of the transom and gently slope upward. That means the drive train becomes 1 ft longer than with surface piercing props.

Covering the external contraption with a platform is a good idea.
It adds strength and safety, if you design it properly the steering hardware can be installed in the hollow platform (like Simplicity Marine does).

Which way you go depends on your skills with grp work and mechanical constructions, available tools and your attitude towards challenges.

 

CDK thanks!

After sitting in the boat for about an hour last night, and seeing the 1.9 size in person, Im pretty sure thats the way I want to go.

With twin setup, ( as opposed to single and an outboard backup/trolling) I have less weight, a single type of parts to source/keep on hand, single fuel type on board, no extra platform or bracket on the back or getting controls bak there. Costs should be close to a wash I think.

Next is the prop placement. I dont want doghouses at the stern. As small as the 1.9's are, and if I put them up near the bulkhead where the 350 used to be, I have 7' behind them to the stern. That should be enough room and not have to modify the hull?

Im not engineer enough to figure that part out yet. 15 degrees currently on the existing. Isnt there enough room to get the right size prop without tummels? The old setup only had room for a 4' shaft.

With all that said, Im getting closer to cutting some fiberglass I think! The tech stuff.

The 1.9 are rated at 100 hp. Can be tuned up another 30% in the computer.

What size prop? Shaft?

What transmission and ratio?

How much fuel to plan for? TDI rated 40mpg plus. The gasser was 10mpg, (mpg just for comparison)

Uh oh, Im going to be late for work if I type more.

Thanks guys!

 

Transmissions 2:1, reverse also 2:1 so one can turn the prop counter clockwise. Technomarine TMC345 (part of TwinDisc) seems like a good choice to me, that is good value for money. SAE flanges and engine couplers from the same company.

Props 14", pitch to be determined later.

Make sure they sell you the TDI's with their MMU (black box) and wiring, they do not run without it. Both must have the same engine code.

You won't hear from me for about a week. No lack of interest but I'm taking a short holiday!

 

Thanks CDK,


Enjoy that holiday! BTW, at 14', like I have now, I wont have to modify the hull, other than changing from one shaft to two! That will be great!

 

Hi Chris, got your message, but it has been a bit turbulent lately here (one of my daughters gave premature birth to a new sailor, causing some worry), so I have not had the time to focus on your project. A quick browse tells me that neither the single Cummins nor the twin VW's installation should present unreasonable problems, provided the structure is capable to cope with the loads. But give me a day or two and I will be back!

 

Will do. Thanks!

 

One question: I didn't see which Cummins version you were talking about, we need power at rpm's for a start.

 

it is a 2004 5.9 24 valve TD. The nfo according to Dodge is;

235-325hp @ 2900 rpms
460-610 ft lbs @ 1600rmps

The VW 1.9 stock s 100hp, but changing the pump to manual can also have 30% hp added for a few $. I read online that some do thngs to get over 300hp. Im not that kind. Twin 130's woud suit me quite well

 

Ok, that is quite a wide span. I understand the power has been changed over the years, so again (sorry to nag...) WHAT POWER IS THE ENGINE YOU HAVE AT HAND?

Then, the weight you have given is dry weight for auto version w/o heat exchanger and marine transmission. With the marine paraphernalia, the weight is ~625 kg (1370 lbs). I guess your weight figures on the VW engines are likewise auto version?? With oil coolers, heat exchangers, sea-water intercoolers, transmissions, shafts, couplings, props, brackets etc etc, there is no weight advantage with the double VW:s, just double trouble.

Anyway, I feel that neither of those arrangements would suit that hull very well, due to the weight. You will have a lot of work to turn this shell into a seaworthy boat, without having to deal with an overweight engine arrangement, causing longitudinal imbalance, plus all the fiddling necessary to find and correctly fit the marine equipment.

If I were in your position here, I would focus on a single engine installation with an "outboard tunnel plus submerged propeller", and start searching for something in the 220 to 250 hp span. There are a number of lighter engines in the 4 á 4.5 l. displacement range. F.i. look around for the VM 4.2 liter six, same engine is used by Mercruiser/Detroit Diesel, painted black. It weighs in at ~450 kg (990 lbs) complete marine equipped.

If you still say that you can have the Cummins for budget money, then plan for a stretch of the boat by moving the transom two feet back, still with an appropriately designed outboard tunnel.

 

I dont have an actual measurement of the Cummins. Its on a pallet. Those numbers are raw from Dodge.

Actually, the VW's are only 265 lbs ea. I found out today. So 530 vs. 1190 net wt.

Building a platform to hide the single prop isnt a problem to me. I need a trolling motor bracket if single anyway. I guess having a second fuel tank for OB isnt that big a deal.

Here is another thought. My fishoholic Sons say I should quit messing around with all this, mount a platform off the stern and go outboard all the way. Yes I have to beef up the stringer/transom configuration. But I have to build that to a degree for the Cummins anyway.

An offshore bracket is $800-$1200, stringer/transom work in conjunction with transom storage etc. another $1200. Maybe the boys are wiser than me?

What about this path?

 

Take a look at the 6.2 or 6.5 litre GM diesel. You will be able to use a 71c velvet drive, 1" shaft and 14" wheel. I have been using this combination for 10 years now with over a thousand hours with the same shaft angle so you will not have to restrut. Osco has manifolds, bell housings and heat exchangers on the shelf for this engine. The owner of Osco has 6.2's in his boat. This engine has the exact same foot print of the GM big block 454. So engine mounts are readily available. If you have any specific question please pm me. Take care.

 

Naah, the VW's are certainly NOT 265 lbs, they are 265 kgs each! And as long as you are paying the fuel bill, your boys are wise enough, but....... . Carterets version is absolutely a clever way to go; there are good quality marinizing parts available for the GM v8.

BUT: the Velvet drives have rather high losses when used with input rpms above ~3000 rpm (servo pump power is optimized for low rpms), and the prop efficiency with 14" dia for this power level is also unnecessarily low, so go for something like a 1.5:1 reduction with a transmission that is not stealing so many of your ponies! That will do good for your wallet and you will still (?) be the wise ol' man!

 

First I was told the 1.9's weigh about 400lbs. Then reading the TDI forums, the said they weigh 265..... Information is all over the map.

I was also told the 4 stroke OB are fuel efficient. No? Im about ready to just buy an aluminum sled and go fish. This project is mostly about the challenge, so I really dont want to bail out.

Almost a year of going back and forth on options is getting old. I want to get to building.

 

What are you paying for gasoline and diesel fuel respectively?

 

$2.98 for gas and offroad diesel is about $2.65 Guessing by taking .40 tax off of retail.