repower for 1969 46 MY

The story on my new 46 Roamer was that it originally came with 8v71 power, which got swapped out to twin turbo and intercooled 543ci SeaMaster gassers. The more I look at this thing, though, the more I'm convinced it was originally a 427 gasser. The fuel tank doesn't have a return line or even a port where there might have previously been a return line. That almost certainly means it wasn't a diesel.

Then there's some paperwork I found that indicates 427 power. It's not the original build sheet so from a provenance standpoint isn't especially reliable. BUT, taken along side the fuel tanks I'd say it supports the theory that this boat has always moved with gas power.

The deal is, I've been thinking repowering "back" to diesel ever since we found this rig. Just yesterday, a local boatyard owner called me to report that he had a pair of 6-71TIBs w/gears for $2500. As you would imagine, one of the engines needs a cylinder head and cylinder kit on one jug. The other engine needs oil/fuel coolers. I can't imagine getting 930hp for any less.

The old SeaMasters will come out over the next two weeks, along with a bunch of other junk. I haven't decided for sure about the TIBs, but any thoughts on the matter would be appreciated.

Cheers,

Q

Well, this isn't the first large Chris yacht I've owned so this stuff isn't a complete and total stab in the dark for me. These are without a doubt the original tanks. The fuel tanks were obviously not steel or aluminum but I didn't have the acid kit to test the material last time I was on the boat. Then Mark came along and mentioned monel and the lights went on.

The fuel lines are original and are sized for gas, not Detroit Diesels. Like I said, there were no return lines, which screams gas. The list kinda just goes on. The fella in Alex VA (Eric? Alloyed2sea?) provides specs for each model and 427 was listed as one of two possible power options in these 46s. The final bit that has me convinced is that Jim Wick wrote back and said the HIN comes back as a 1969 46 footer with 427 Ford pahwah.

So, the info I got from the guy who's selling the boat saying that this beast had 671Ns originally was urban legend at its best.

On the upside, a guy called me today who is interested in the twin turbo SeaMasters. Hopefully he'll show up with a trailer when the crane yanks 'em out next Thursday. If not, it's ebay or the scrap metal yard. There must be 20 pounds of copper in each of the exhaust risers alone.

The boatyard owner who has the TIBs is a buddy of a buddy and we've met before. He kept them after repowering the boat they came out of rather than selling them off as cores or scrap because, he claims, one only needs a head and a cylinder kit (rings, actually, which he claims look like Chiklets, but if you're already in there...), and the other engine needs fuel & oil coolers and other bolt-ons. The guy's not an idiot, so I can't imagine that he would have kept junk motors on spec. I haven't seen them in person yet, but the guy's trustworthy. Which is not to say that I'm definitely going that way, but hopefully explains why I'd even consider them.

The shafts look to be 2", which are well within the range for the way I will use the boat. Boatdiesel's calculator says 2.31" is recommended for 465hp, but that's with a safety factor of 2. Since I would derate the engines to match the cruising we do 99.9% of the time, there's no reason to go with rated shafts.

There are two sets of props (3 & 4 blade, the latter is 24x24) but for my purposes I'd need larger ones anyway. Something between 28 and 30" is what I'm considering. The exhaust looks to be 6" right now, which also appears to fall within specs.

But the raw water intake is on the wrong end of the engine and might be too small. Then again, I was on a 60 Roamer w/12-71TIs and was startled at how small the seacocks, strainers, and raw water plumbing was--like, 2" or so. That's smaller than what's on my current 52' Connie w671s! I'll already have a welder in for a day to do engine mounts, block off a few old transducers, and zip up some pits. In the grand scheme of things I doubt the cost of relocating and installing new raw water plumbing will be that much.

There are a few issues that pretty much kill the idea of keeping it gas: E10 and soon to be E15 & E20's got a shelf life that's less than milk. Equipment durability. Increasing risks w/CO &/or sparky boom-boom. Webasto diesel hydronic heaters don't burn gas... The list just kinda goes on.

Plus, I like the sound of 6-71s. VROOM!

OK, we're back to powerplants again. It turns out that the shafts are actually 1.5" and the exhaust is 4"ID. That means that the max HP that can be run on this boat without $ignificant upgrade$ is about 350 or so.

Here's the line-up:
New 300hp Nanni (Toyota) diesels are $40,000 (engines, gears, mounts, wiring & panels)
New 200hp Nanni (Toyota) diesels are $30,000 (engines, gears, mounts, wiring & panels)
New/factory reman 300-330hp Cummins are $25,000 (engines, gears, mounts, wiring & panels)
Used 300-330hp Cummins are $20,000 (engines, gears, mounts, wiring & panels)
New/factory reman 210hp Cummins are $20,000 (engines, gears, mounts, wiring & panels)
New/factory reman 160hp Cummins are $17,000 (engines, gears, mounts, wiring & panels)
475hp (derated and governed to 300hp) 671TIBs w/gears needing cylinder kits + ??? are $2500

And--don't laugh, I'm looking at every option and keeping in mind that we rarely cruise faster than 10kts in our current vessel--zero hour 90hp Ford Lehmans w/gears for $3,500 for the set.

Buc book says the Retail Price Range for these boats is $86,800-$95,400, which puts the 300hp Cummins & Nanni options into perspective. I'm looking at the price of diesel, the speed we tend to travel at almost all of the time, the cost of the repower, and ongoing operating expenses and trying to figure out why the Lehmans are the wrong way to go. I mean, 1.5GPH @ 7kts is what many folks claim out of the 90HP Lehmans in single-engine "fast trawler" applications (i.e. same basic hull form as the Roamer but without the drop dead sexy lines up top). Between 4,000 and 10,000 hours is not uncommon with unstressed Lehmans. And according to some calculators at boatdiesel, 180HP total onboard would yield a comfortable cruise of 7-8kts and a max speed of 11. What's not to like?

Or, put another way--what is it about new Cummins or Nanni that would justify 10x the price of the Lehmans if we're pretty much always putzing around at 7-11kts anyway?

"perfectly good pair of Cat 3116's "

HA! Now there's a contradiction in terms if ever I saw one! lol

Seriously, I've also talked with somebody who runs 370hp Cummins in their boat with 1.5" shafts. As far as the shafts go, I've always heard that materials may be just as important as diameter. It would be interesting to see what these shafts are made of.

The biggest problem I see with any kind of gas powered cruiser is that e10 seems to have an incredibly short shelf life. e15 will be shorter and e20, when it gets here, will be shorter still. I don't see gas as a viable option for this and several other reasons.

Seafarer, my experience is primarily with semi-displacement hulls. But having corresponded with a couple of 46 Roamer owners, it appears as if calling these big yachts planing hulls is a tad over-optimistic. As far as the ill-handling planing boat at displacement speeds theory goes, I think there's an awful lot of misinformation and urban myth out there. When we putz along at 8kts in our Connie, things are more or less dead flat. The notion of handling doesn't really apply. When in nasty weather, we do what my old man always taught me to do--keep it slow. Now, if we were running at the speeds you're talking about (i.e. in that nasty region where you're way above displacement speed but nowhere near planing), the story probably changes. Personally, I've never been in the habit of running at those speeds.

There is a fellow on a Hatteras forum who, with 12v71TIs in a 61-footer, manages up to 3nmpg by running his vessel at the speed he has modified it to run at best--around 9kts. Running that semi-displacement boat at WOT, he manages somewhere around 0.5mpg. This is not unlike what I have experienced in my 52 Connie. I have a hard time believing that 16-ton Roamers pop up on plane so well that they would not achieve maximum efficiency at true displacement speed rather than the maximum hole-diggin' speeds you give as examples.

Unfortunately, this Lehman idea won't go any further. These engines, I've learned, are pre-Lehman Fords. They are apparently much smaller blocks than the Lehmans were. The search continues...

It would be helpful, though, if some other 46 Roamer owners would chime in with their shaft, exhaust, and HP numbers. From what I've heard so far from them, none of them approach 3nmpg while mashing the "loud sticks" forward.

I'm curious, Seafarer--what are "8v71 naturally aspirated 318's"?

Cheers,

Gotcha. I've always heard of that version of the 871s as 320hp.

Without input from owners of sister ships to this one, it's difficult to say when the boats begin to plane. Again, with my 52 Connie (a narrower and longer boat) the ride is very pleasant at hull speed.

The beauty of the particular Hattie guy's experience that I mentioned was that he went to bigger wheels with more pitch and derated his governor to WOT at 1600rpm. THEN, he put pyrometers and pressure gauges to the engines to see exactly what improvements happened. The proof's in the results even if it's counterintuitive to folks who believe that the engines in nondisplacement hulls must be pushed to 200 ticks off WOT--slow speed running coupled with proper loading at the prop yields very happy older, heavier engines and fabulous economy.

Little of this helps for my boat, though, because the wimpy 1.5" shafts I've got (assuming they're 304SS) can take no more than about 160 slow-turning diesel hp. High revving diesels like Nanni or Yanmar are good for up to 300hp, but who cares since we normally putz along at hull speed? Hence the interest in low output Lehmans, particularly since this is the last boat I ever intend to outfit.

acellist, thanks for the numbers. I love the shot out the transom window.

1.5" shafts with 871s? Hmmm...that leads me to believe that the shafts are not made of 304 stainless. Your exhaust sizing tells me that these boats were purpose-built for the power they originally came with. A sister ship to mine (ie 427 gas-powered) also came with the 4"ID pipes. So, given that I'm not interested in refitting shafts or exhaust on this boat, the limiting factor to the max HP I can install is the exhaust (assuming gas boats came with shafts of the same material as diesel boats).

OK, so with 640hp on tap you can and do thunder down the river at 20.5mph. Tell us, what speed to you tend to travel at and why? Also, at 10kts or so does your boat handle like a pig?

Cheers,

Excellent write-up, acellist. If I recall, you averaged just about 1nmpg on that trip.

Funny thing about the 90hp set of Lehmans...they burn about 1gph while producing sufficient power to theoretically push this boat along at about 8-9kts. That's about 4x the fuel economy of your average Hatteras LRC 48, which came with twin DD 4-53 @ 110hp.

If you haven't experience bad handling at less than "planing" speed, I'm feeling a little bit of love for these fuel sippin' Fords.

Seafarer, I don't understand what you mean. What Huckins thread and what quotes?