Inboard options 6.0 vs 5.7 vs Diesel

[Briguy]

A while back I considered a Diesel Jackshsft conversion for my boat with a Bravo.
All in it would have been 27k. Glad I didn't with the advance of 4 stroke outboards.
Yanmar also offered a 6 cyl 250 go that was smoother and had a lot more torque then the 4cyl 240. For an inboard application I think either would be bad ass. A few years ago there was a Sceptre with a 300 Yanmar for sale in Tampa/St Pete. Don't know whatever
happened to that boat.

[OSEAD23]

Thanks guys! Does anyone have an idea of what a yanmar by260 costs? i think that may be what you are talking about as thats their new engine in that size..
that looks like the best option in a yanmar. BTW it weighs less than a 5.7 gas engine by 200lbs too.

any other ideas on other diesels in this size range?

jim

[Highway12]

The 6 cyl would be a really tight fit in the 23. The 260 is a marine conversion of a BMW motor. Full of electronics in a hull that always seems to have some water in it. It's a shame they had to stop the 4lh series in the US, it really is a perfect motor for the inboard. Light, plenty of power and sips fuel. The boat will stay on plane at 11 knots. At that speed the boat can handle some pretty nasty seas that most small boats could not. I think thats what makes the inboard so unique.

[OSEAD23]

Highway on your 240hp yanmar what prop and transmission gear reduction are you running. I was speaking with someone that has a 240 available and after some research on his part he was recommending a 1.2:1 ratio. I have a 1.5:1 on the gas engine and i run a 16x16 4 blade or a 17x17 3 blade. The 16inch diameter is much quieter. I ran the numbers on a prop calculator called Vic prop and if i follow them the 1.2 seems right since the max diameter I can run is 17inch which does rumble a little. With a 1.2:1 they came up with a 16x17 3 blade. With the 1.5:1 they came up with 18.5x 21 3 blade or 17.5 x21 4 blade.

btw they come up with a top speed of 31Knots which it seems you are doing better.

jim

[Highway12]

I'm running a Borg Warner Velvet Drive 1:5:1. and 3 blade 17 x19 wheel. Mack Boreing sold me the bell housing and torque converter for the gear. I only had to make some slight adjustments to the existing stringers and used the existing shaft and coupler. You can see pictures of my boat and installation under albums in the community section (at least I believe they are still there). I find that the Diesel actually works better than the old gas motor with the tunnel. The prop rarely ventilates, the added pitch seems to hold the boat in the water better.

[Fr. Frank]

Originally Posted by pelican

a stern drive - hard to believe,IS more efficient than a straight inboard...


multiport motors are more efficient - freshwater cooling helps too

repowering is a little more than just dropping a new motor in and hooking it all up.taking the time to get things right and actually improving the boat is what it's all about - that's what seperates a true repower from an engine replacement....

and more efficient yet is a Weissman counter rotating dual-prop surface-piercing drive with variable pitch propellers, but who wants to spend $170K on just the drive system for a 23' boat?

[jnamowitz]

Does anybody run a Diesel sterndrive? Im looking at converting mine. I love the weight of the engine in the boat and I think and outboard with bracket would drastically change the ride.

[Briguy]

How exactly do you ventilate a pocket?

Originally Posted by OSEAD23

I want to thank you all for the information. I have been leaning on going with the 5.7MPI for most of the reasons you all mentioned so thanks for that. I wanted to make sure I wasn't sacrificing additional performance potential with the other options. I know this wont be as fast as an outboard or an i/O but a few Knots are nice on a 60mile run each way as we often do.

I spoke to some one who has designed Hulls and race boats today and he mentioned that one of the reasons the inboard pocket boats runs slower is that the pocket and prop work together like an enormous pump sucking water into the pocket and essentially causing you to carry hundreds of gallons of water with you as you move along and at a certain point the horsepower and torque as useless in creating more speed or forward motion due to this. He did mention that ventilating the pocket is something that has been shown to increase speed as it breaks the suction in the pocket.

Again I am not looking to make the boat something it cant be just the best it can I dont get to use it enough on blue bird days and it would be airborne most times on most other days because of the sea conditions.

At this point its looking like a new 5.7 mpi

Jim

[FLexpat]

Originally Posted by jnamowitz

Does anybody run a Diesel sterndrive? Im looking at converting mine. I love the weight of the engine in the boat and I think and outboard with bracket would drastically change the ride.

I replaced my wrecked Alpha with a Bravo 1X Diesel drive so I could have the option in the future. Boat isn't done yet and I have a 5.7/260 with only 380 hrs but if an appropriate diesel showed up I would do it. I think the biggest challenge would be getting a bellhousing for the Yanmar that would mate to the Merc transom housing. Merc has a 4.2L 370HP v8 diesel that is intended for that application - I think it is the VW or BMW motor but when I looked into it it was pretty pricey.

[OSEAD23]

You can ventilate by putting a thru hull in the pocket with a pipe or tube that is open but above the waterline. when you run a vacuum is created and the open tube inject air into the pocket breaking the suction. Of course the suction does hold you to the water and is probably one of the reason the inboard rides so well. I haven't done this because of all the variables..


jim