Hey all, I just had a 1970 Hatteras 36’ sportfish just pop up for sale in my area. It has no engines and I’m dreaming of doing a possible conversion from a fast boat to a trawler. It’s a twin screw boat so I was thinking a pair of 30-40 hp diesels would be a good fit. Thoughts? It ran with a pair of 6-71 Detroits and the previous owner was going to put a pair of Cummins 5.9’s but has decided they no longer want the boat.
36 Hatteras possible trawler conversion
- Thread starter Jmk2000
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Comodave
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Well…. The first issue I see with that plan is that you may kill any resale value of the boat with those small engines. If that is a concern then don’t do it. If you don’t care then proceed with the planning stages and see what performance you might get with those small engines. Will you be able to handle a severe windstorm and associated wave with that little power in a hull that was designed for much more power. That is off the top of my head without doing much thinking about it.
OP, okay so poor resale, not zero, but your pool of customers will be greatly reduced. There will be however others who may be interested in your vessel type.
However... running a planing hull at displacement speeds will exhibit poor tracking and ungodly roll. That hull form relies heavily on dynamic stability. The hull likely has little or no keel. Absolutely you will need to create much large rudders - hope your fiberglassing skills are strong.
A semi-displacement hull would be a better bet and most have some semblance of a partial-keel to help with tracking, but would still benefit from larger rudders.
Anyway I really like your idea but you might want to consider how to build an enlarged keel, deeper to protect your props, as well as the rudders of course. You'll still get pushed around in following and quartering seas.
What engines are you considering, a couple of small Kubotas or Doosans from generator sets?
However... running a planing hull at displacement speeds will exhibit poor tracking and ungodly roll. That hull form relies heavily on dynamic stability. The hull likely has little or no keel. Absolutely you will need to create much large rudders - hope your fiberglassing skills are strong.
A semi-displacement hull would be a better bet and most have some semblance of a partial-keel to help with tracking, but would still benefit from larger rudders.
Anyway I really like your idea but you might want to consider how to build an enlarged keel, deeper to protect your props, as well as the rudders of course. You'll still get pushed around in following and quartering seas.
What engines are you considering, a couple of small Kubotas or Doosans from generator sets?
portager
Senior Member
The original 6-71 DDs were over 2,000 lbs each. Without a comparable amount of engine and/or ballast weight, she may be tippy. There is no interior pilotage, just the flybridge, so she would be a fair-weather boat and all your passengers will be in the flybridge underway.
Gdavid
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There is a forum member here "Ken E." that has repowered his Hatteras 45' from 871's to 210 HP Cummins 6BTA's (5.9L). He is happy with the results, this is a less drastic reduction in power to what you are considering. Hopefully he will chime in. If at all possible I would try and stick with something larger than 40 HP, a pair of NA 5.9's rated at 150 HP would be a good compromise if they fit your buget. If you go down to 30-40 HP, and I suspect you would need to swap the shafts to something smaller and lighter to avoid stalling them out when you are shifting into gear.
mvweebles
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Will need to change props too. Small rudders won't help your cause either.
Sportfish to trawler may be a bridge too far.
Peter
Sportfish to trawler may be a bridge too far.
Peter
Gdavid
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Sportfish boats do spent a lot of time running about 7knots in snotty conditions when trolling, so what you are considering isn't crazy but when running an inlet, having the power to bring the bow up is something I would want to retain. The boat may not need to reach planning speed, but I would want it capable of at least 12 knots. I fished on a 47' Jack Hargrave designed sportfish, I believe he designed the Hatteras 37 as well, spent a lot of time trolling anywhere from 2.8 to 8 knots, boat handled fine, at the lower speeds, most of the time it was running on 1 engine.
rslifkin
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Swapping in the Cummins wouldn't be a bad thing for using it as a trawler, especially if they're the later electronic Cummins (which tolerate light loading well). In a hull like that, you can run slowly 90% of the time, but the boat won't be at its best in certain conditions without being able to speed up a bit. And the small diesels will only save a little bit of fuel compared to the bigger ones, plus, as mentioned, you'll have more weight to make up compared to the heavy Detroits that were in there previously.
We have a similar size planing hull, not drastically different in hull shape than an old Hatteras (primary difference being a more full bow on my boat). We also have decent size rudders. Typical cruising speed for us is 6.5 - 7 kts, even with big engines meant for planing. We can happily cruise at 17 kts, but we only do that occasionally. The lower fuel burn and quiet at lower speeds is well worth it, and in most conditions, our boat handles just fine at low speeds.
We have a similar size planing hull, not drastically different in hull shape than an old Hatteras (primary difference being a more full bow on my boat). We also have decent size rudders. Typical cruising speed for us is 6.5 - 7 kts, even with big engines meant for planing. We can happily cruise at 17 kts, but we only do that occasionally. The lower fuel burn and quiet at lower speeds is well worth it, and in most conditions, our boat handles just fine at low speeds.
Pete Meisinger
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Not really a bad idea but consider ballast and increasing rudder size. Make sure you get it for a good price because resale will be down.
pete
pete
Good point about the weight differential. Ballast could be in the form of a huge bank of FLA batteries distributed at the chines port-starboard. Either 8Ds or even better, a bank of 2V OPzV/S. Now your trawler will be cruising with about 30kWh of battery bank.
Sounds like a fun project, so get creative.
Sounds like a fun project, so get creative.
mvweebles
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A 1970 36-footer with no engines. How do you figure resale could go any further south????
Peter
rslifkin
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Even with bigger engines there will be lots of weight to make up. The old Detroits were heavy, so even the previous owner's planned pair of Cummins will be easily 1000 lbs lighter (total) than the original engines.
Ken E.
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In northern BC presently with my boat, arriving in Ketchikan AK in two days. As GDavid mentioned, I removed 871 Detroits replacing them with 210 Cummins in my 1971 45' Hatt convertible. I did this nine years ago and it has turned out great for my application.
A couple very strong provisos, though. Doing this will cost you a lot of money that you will never get back on resale. Never. The only way it makes sense to repower a boat that old is if the boat is a long-term hold, maybe your last boat. In that case you will recover the cost through the use of the boat and the utility it gives you. For me, up and down to SE AK with low-time engines and gears is worth a lot. I did a lot of the work myself on the re-power but the hard costs, recon engines and gears, started me at $100K. But it's so much more than that. Motor mounts, exhaust run, wiring, countless changes. And I had to re-ballast the boat. A bobtail 871 weighs 3000 lbs, roughly. A 6bt 5.9 Cummins weighs 1000. I took out two tons of weight way down low and the boat became very tender. I talked to Hatteras and put the weight back in with their advise on placement and the boat is now true on its lines and feels stout.
I can empathize with you wanting to do this with an old Hatt. The '70's Hargrave designs are the best of the bunch to me. It always rings my chimes to look at my boat's shearline and profile. But give yourself a reality check before you embark on this. Lots of money involved that you'll never see again. You have to REALLY like the boat to do this.
sean9c
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The boat better be free or better yet come with some cash, a repower will cost way more than the boat will be worth and that's if you do all the labor yourself. Paying someone to do it would be nuts.
The hull is definitely a semi displacement/planing and thats exactly what I was thinking, a couple of Beta’s (Kubotas) or yanmars.
There is controls within the cabin. The fly bridge is currently removed. If I get it I might decide to leave it off all together
Lol it’s a big factor of why I’m so interested. It’s a good price for a hill that’s in great shape. It’s a blank canvas
Definitely fair advice and I really appreciate the reality check. If I took it on I totally understand the money aspect. It’s a project boat for sure, I’m dreaming of doing the great loop and making this my bot for a lifetime
Hey, you're converting a sportfish into a "trawler" of sorts, so go for it and have fun. That space up there provides you with a huge area for a solar array, which is invaluable for cruising away from dock. There's another thread where @Dashash documented a similar modification and it looks great.
https://www.trawlerforum.com/forums/s3/remove-flybridge-add-solar-61505.html
Hey thanks for the link Mako!
Gdavid
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There is a Hatteras 34' for sale, I believe near Crisfield, MD (Facebook marketplace) with running 4-53's, removed flybridge, and looks rough but usable for $30k. It would be much cheaper in the long run and the savings would offset a lot of fuel costs
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What is Phelps? I’d be interested to see it if it’s boat you converted
Try searching for "Cummins." The engine manufacturer's name is spelled without a "g."
engines - here is some used ones advertised
Link to a couple used Cummins Engines with Transmissions.
Not my items, just saw them so sharing.
$ 36,000.00 for both.
https://www.2coolfishing.com/thread...or-36-000-for-the-pair.2711565/#post-24099916
Good luck.
Link to a couple used Cummins Engines with Transmissions.
Not my items, just saw them so sharing.
$ 36,000.00 for both.
https://www.2coolfishing.com/thread...or-36-000-for-the-pair.2711565/#post-24099916
Good luck.
