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

[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]

Originally Posted by 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)

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) 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

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.