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