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Viking 1973 40' repower

Old 10-18-2019, 06:50 PM
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Default Viking 1973 40' repower

My dad is considering doing a repower for his 1973 40 foot Viking. He is considering going with Cummins, the boat currently has twin cat 3116 engines. We currently hit about 10.5 knots at 2100 rpm (he just bought the boat and we don't yet know the prop pitch etc.) . Is there a calculator that we can use to figure out how many horsepower we need to get to for a target speed? We are trying to get to around low 20s Cruise speed and close to 30 for wide open throttle. Any help is much appreciated. Thanks
Old 10-18-2019, 07:19 PM
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A friend of mine re-powered the same boat, he opted for Yanmar. I think that they were the 550HP. From what I can remember, he got about 23 knots at cruise and 28 top speed. The Yanmars sipped fuel.
Old 10-18-2019, 07:22 PM
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Originally Posted by nfairbank View Post
A friend of mine re-powered the same boat, he opted for Yanmar. I think that they were the 550HP. From what I can remember, he got about 23 knots at cruise and 28 top speed. The Yanmars sipped fuel.
Any chance you can find out what they were? He just talked to a guy today who said consider yanmars. Thanks so much for the info!
Old 10-18-2019, 07:33 PM
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You need to see what props and gears you’re running. If those are 350hp Cats there is something wrong if your only making 10knts. With 6-71 turbos those boats would run mid 20’s and that was with 450hp each. Those hulls are pretty flat on the stern so they don’t take enormous levels of power to run mid 20’s
Old 10-18-2019, 07:36 PM
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They are 3116 and as I understand they are only around 210 hp each. I agree we need to check on Prop pitch and gears. If he does the repower he would also do the Transmissions as well.
Old 10-18-2019, 09:48 PM
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If you join Boat Diesel’s membership they have some programs that you can run simulations that are surprisingly accurate. You will need to know vessel waterline length, weight and hull shape. The shafts in that model Viking were a little on the light side so you may need to step that up. Most engine manufacturers have installation blueprints online. You may have to go to a down angle gear to get the front of the engine under the deck
Old 10-19-2019, 12:01 AM
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Originally Posted by dsharp View Post
If you join Boat Diesel’s membership they have some programs that you can run simulations that are surprisingly accurate. You will need to know vessel waterline length, weight and hull shape. The shafts in that model Viking were a little on the light side so you may need to step that up. Most engine manufacturers have installation blueprints online. You may have to go to a down angle gear to get the front of the engine under the deck
Great thanks, I will check into that.
Old 10-19-2019, 05:36 AM
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If you are doing a repower I wouldn’t consider any engine but Cummins. The 540 or 600 QSC would be a good match for that boat. Here is a thread from my repower a few years ago:

Bertram 36 Moppie Repower
Old 10-19-2019, 05:52 AM
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Glad to hear, thanks. We will definitely check out your repower.
Old 10-19-2019, 08:12 AM
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Originally Posted by Wallers View Post
They are 3116 and as I understand they are only around 210 hp each. I agree we need to check on Prop pitch and gears. If he does the repower he would also do the Transmissions as well.
I could be very wrong but I believe the 3116 lowest power rating in a marine based engine was 300. There were also a lot of 350hp versions installed in boats up to your size. The short of it is that engine does not do well from either a performance or longevity standpoint in vessels of your size. I have 23 year old 3116s in my boat with mid 3,000hrs. I have discussed pulling them and dropping in factory re-mans just due to age but am holding out for a possible switch to 7.1 remans down the road. I would have no issue putting 3116s back in my boat but in your situation I would absolutely not consider a 31xx series.

I am no expert but I'd think your easiest/best repower would be 375hp 3208. Definitely not a 30kt boat with them though.
Old 10-19-2019, 07:23 PM
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Cummins c series (450HP) or Cummins QSM11 is what I would repower with
Old 10-20-2019, 08:37 AM
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I have a friend with the same boat with 485 Detroit 6-71's, I think later DDEC's. Anyhow, your going to need something around 450 each side to hit your speed target. We cruise a 40 Ocean at 24 kts with CAT 3126's at 420 / side.
Old 10-20-2019, 08:47 AM
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Good to know, that's helpful thanks.
Old 10-20-2019, 08:54 AM
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What rpm and speed do you get at full power? And yes, I don't think the 3116 was offered at 210hp in marine form. All I have seen is 300 or 350. Might be some commercial marine rated lower, but rare in private vessels.

With hp rating and full power rpm and speed numbers, better advice can be given.

10.5kt at 2100 sounds like it stuck on the hump.
Old 10-20-2019, 09:17 AM
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Originally Posted by Corndog38 View Post
What rpm and speed do you get at full power? And yes, I don't think the 3116 was offered at 210hp in marine form. All I have seen is 300 or 350. Might be some commercial marine rated lower, but rare in private vessels.

With hp rating and full power rpm and speed numbers, better advice can be given.

10.5kt at 2100 sounds like it stuck on the hump.
We didn't get a lot of information from the guy we bought it from, and we are trying to check in on the engines. We get to around 12 knots at 2500 rpm. That is as high as we can get it
Old 10-20-2019, 09:42 AM
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Could the props be fouled with bio growth? That would easily explain not getting speed and rpm.
Old 10-20-2019, 09:45 AM
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Very possible, we will try and dive on it this week. It is getting hauled around Thanksgiving, so I would like to try and rule it out before he has it hauled. Thanks
Old 10-20-2019, 10:21 AM
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Originally Posted by Wallers View Post
We didn't get a lot of information from the guy we bought it from, and we are trying to check in on the engines. We get to around 12 knots at 2500 rpm. That is as high as we can get it
They may be 3160 cats. They were rated at 210 HP when naturally aspirated. I don’t remember when they came out with the 3208. Are they v-8 engines on inline 6’s?
Old 10-20-2019, 11:00 AM
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Originally Posted by dsharp View Post
They may be 3160 cats. They were rated at 210 HP when naturally aspirated. I don’t remember when they came out with the 3208. Are they v-8 engines on inline 6’s?
that's my bad, they are 3160s, I just checked with my dad, which matches the 210 hp number I was told. Sorry about that.
Old 10-20-2019, 11:14 AM
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The 3160 is the predecessor to the 3208, same bore and stroke. Probably original to the boat. I don't think they turbo'd the 3160, so 210hp is about right.

Gonna be a slow ride with those motors, but do check the running gear to see if it fouled. Still probably going to be a 15kt boat with every thing right and clean bottom/props/rudders.

More power would be nice. But go too much more and you are going to need bigger shafts, which can be pita and $$$.

Without knowing any more, gut feel is the QSB 5.9 380hp gets top of the list. Those recommending the QSC 550, 600 or (gad) QSM 11 for a 45yr old 40 footer are nutz.

3208 Cat at 375 should be on the list, but it is long out of production so what is on the market might be sketchy, wore out or have crappy rebuilds.

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