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Old 01-26-2020, 09:38 PM   #1
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Should I Mainship 34 mkII

I have an opportunity to buy a mainship 34. It is being sold as a 77 but from the pictures it looks like a mkII which would put it at a mid 80s boat from what I've read. The previous owner passed away part way through a refit and his wife does not have alot of info for me. My questions are as follows. First the boat has a cat 3208 with 325hp. Is this too much hp for this hull? Will this motor get good fuel economy? The boat has a new 1.5" shaft and prop but has been in the water for 3 years, are they going to be damaged without the zincs being changed? The motor was installed 10 years ago but is started regularly (200hrs) but the boat has not moved. I have a ton of questions but these are my main concerns. I have included a couple pics so you can see why I would consider finishing a refit started 10 years ago! She looks like she has good bones! What are your thoughts thanks for the input!Click image for larger version

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Old 01-26-2020, 10:05 PM   #2
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Yes, 325 hp is too much for that boat. I remember reading an account of someone who repowered his 34 with a Cummins 210 or may be 270 hp. He said at 18 knots it got squirrely, bow walking or something. So you need to keep the speed down to the lower-mid teens. But at that speed, say 15-16 kts that engine will purr along and last a long time.

But no mater, if you don't want to go fast that 325 hp engine will run just fine much, much slower. It may burn a little more fuel than a smaller engine at the same low hp, and you may not even be able to measure it, maybe 1/2 gph more at 7 kts than the original Perkins. This is due to its larger displacement than the Perkins.

Wow!!! That is some clean engine room.

Leaving the boat in the water with no attention to the zincs can ruin the prop due to dezincification- a form of corrosion which pulls the zinc out of the alloy and leaves a pink color. It also loses strength when this happens. The same thing can happen to any thru hulls and valves. Replacing a prop might cost $2000 or so and maybe $500 for each thru hull, but not the end of the world.

An out of the water survey will easily identify these issues so you can budget for them. Also look for soft decks, leaks around windows and rusted fuel tanks (or are the tanks SS?), typical issues for boats of this age.

Looks like good bones to me as well. It needs a bikini over the fly bridge and I would also add a bimini covering the aft cockpit.

Good luck with her.

David
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Old 01-26-2020, 10:49 PM   #3
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The fastest mainship 34 on the internet has a Cummins 315 and can go 20 knots. Theres a video on youtube.

Too much power? Not really a thing. Run it as fast as you're comfortable with but them being sketchy above 16knots is well documented(i'm sure that boat could go 18-21knots.

Economy should be good if you run it like a trawler at around 7 knots.

Whether or not you should buy it is up to you and dependent on price but I doubt you'd run into any major issues with it. It could also do double duty as a fuel efficient offshore fishing boat with a fast cruise and good mpg.
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Old 01-27-2020, 06:31 AM   #4
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Cheasepeaker, I'm assuming you've seen the rest of the pictures of the boat in it's current condition? The 2 you attached show it in a best light. The owner seemed to have very good intentions & it looks like the projects he started were done very well but whew, there are lot's of projects that need completing before it's usable. There's a ton of extra parts that were included to complete it ,but still, it's a huge undertaking. I haven't physically looked at this boat but know about it and have a friend who has looked at it. It wasn't what we were interested in when we were Mainship shopping so I never checked it out.
Regarding the 3208, I wouldn't be awfully concerned with it because the weight is still slung low in the boat & the stability probably hasn't been affected too much plus the II's tank is a single in the aft under the cockpit so that opens up the engine room to be able to get around the whole engine. I believe 34's did come with a Detroit option and the weight was probably the same as the Cat. I would love to have the extra horses...the throttle takes care of the "too much" horsepower issue...
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Old 01-27-2020, 08:05 AM   #5
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The "model II" (not MK) was built from 1978 thru 1982 along with the model I.
In 83 they changed to the model III.
Standard engines were the Perkins 160, and Mitsubishi 200, then the range 4 series with the Perkins 200 and probably some Perkins 165s.
Yes generally speaking these boats get squirrelly above 16 knots, however, the model II had a fuel tank under the cockpit floor and could possibly gain another knot or so before it gets unstable.
I don't think 325 is too much power. As mentioned above you don't have too run at WOT. You'd probably be able to cruise all day at 16 knots and not be pushing the engine. You'd get decent economy as well.
I had a model I that I repowered with a Cummins 6BTA 270 hp. The boat would do 18 1/2 knots at WOT. I could cruise that boat all day at 15 knots and be just under what Cummins backed as continuous RPM rating.
If you buy the boat and have vibration issues (which I did because of the increased HP) PM me because I know how to solve it.
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Old 01-27-2020, 08:08 AM   #6
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Thank you for the good info! If I do go through with the sale and have issues I will definitely pm you.
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Originally Posted by jleonard View Post
The "model II" (not MK) was built from 1978 thru 1982 along with the model I.
In 83 they changed to the model III.
Standard engines were the Perkins 160, and Mitsubishi 200, then the range 4 series with the Perkins 200 and probably some Perkins 165s.
Yes generally speaking these boats get squirrelly above 16 knots, however, the model II had a fuel tank under the cockpit floor and could possibly gain another knot or so before it gets unstable.
I don't think 325 is too much power. As mentioned above you don't have too run at WOT. You'd probably be able to cruise all day at 16 knots and not be pushing the engine. You'd get decent economy as well.
I had a model I that I repowered with a Cummins 6BTA 270 hp. The boat would do 18 1/2 knots at WOT. I could cruise that boat all day at 15 knots and be just under what Cummins backed as continuous RPM rating.
If you buy the boat and have vibration issues (which I did because of the increased HP) PM me because I know how to solve it.
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Old 01-27-2020, 08:10 AM   #7
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Yes I have seen the rest of the pictures from the ad. It definately needs alot of work on it but I am excited about the prospect of finishing the restoration and making it my own.
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Cheasepeaker, I'm assuming you've seen the rest of the pictures of the boat in it's current condition? The 2 you attached show it in a best light. The owner seemed to have very good intentions & it looks like the projects he started were done very well but whew, there are lot's of projects that need completing before it's usable. There's a ton of extra parts that were included to complete it ,but still, it's a huge undertaking. I haven't physically looked at this boat but know about it and have a friend who has looked at it. It wasn't what we were interested in when we were Mainship shopping so I never checked it out.
Regarding the 3208, I wouldn't be awfully concerned with it because the weight is still slung low in the boat & the stability probably hasn't been affected too much plus the II's tank is a single in the aft under the cockpit so that opens up the engine room to be able to get around the whole engine. I believe 34's did come with a Detroit option and the weight was probably the same as the Cat. I would love to have the extra horses...the throttle takes care of the "too much" horsepower issue...
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Old 01-27-2020, 08:28 AM   #8
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We had a 1978 34' Mainship and liked it a lot. Like others have said the extra power by itself should not be an issue. I would be a bit concerned about the 1-1/2" shaft coupled to that hp and torque. Dependent upon the material of the shaft and the selection of prop and cutlass sizes that concern might be larger or smaller.
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Old 01-27-2020, 08:50 AM   #9
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Even tho I am new to this type of boat and engine there are plenty of nightmare stories I have read about people being going for cheaper materials and paying for it. Here is a list of "new" things done to the boat.
*****
**“1977 34’ MAINSHIP”
Work completed to date:
. New Caterpillar engine 3208, Transmission, 1 ˝ “ H.S.S. shaft, & 4 blade prop & engine supports
. New engine fuel filtration-scrubber system
. New built in engine oil removal system
. 3 New bilge pumps ( added 2 more)
. Added engine fresh water cooling piping
. 2 New batteries 2D
. New domestic water & heating system
.New galley sink & faucet
. New galley,**3 burner gas stove & oven
. New galley countertop
. New large refrigerator/freezer
. Installed new electric toilet, emauserater & holding tank
. 2 new power steering pumps, lower station operational
. All new through hull drain
. New electrical panels**& started wiring
. Replaced cockpit door and window with custom size(not caulked to wall so it can be removed for repainting of wall)
. All**new port holes

. New forward Hatch*(not caulked to deck so it can be removed for repainting of ca

*

*


Quote:
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We had a 1978 34' Mainship and liked it a lot. Like others have said the extra power by itself should not be an issue. I would be a bit concerned about the 1-1/2" shaft coupled to that hp and torque. Dependent upon the material of the shaft and the selection of prop and cutlass sizes that concern might be larger or smaller.
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Old 01-27-2020, 10:00 AM   #10
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Who did the work on the boat?
Can you ask them why they selected the shafting that they chose?
Did they use a safety factor of 2 or greater?

Here is a link if you want to read about shafting and formulaes to determine minimum sizes....
Western Branch Metals: Marine Propeller Shafting
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Old 01-27-2020, 10:06 AM   #11
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Lots of good stuff on that list, but no electronics.

David mikki bbn
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Old 01-27-2020, 01:28 PM   #12
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I would also like to know what reduction ratio the transmission is along with prop diameter and pitch.
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Old 01-27-2020, 05:54 PM   #13
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I'd consider the extra hp as a bonus if the install was done well, particularly if you're interested in a fast cruise speed. The repowers that I'm familiar with on these boats included beefing up the stringers and increasing the size of the exhaust system, and reducing the reduction gears from the OEM 2.1 to around 1.5, which reduces the shaft torque and should allow a 1.5" shaft. The best way to harness the extra power over the OEM setup is to increase shaft rpm as the prop diameter can't be increased beyond the OEM 20".

There's some good documentation here on a repower of a M1 with a 315 hp Cummins.
https://mainship34.com/repower/

Looks like a nice project, but do your diligence...
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Old 01-27-2020, 06:11 PM   #14
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I'd consider the extra hp as a bonus if the install was done well, particularly if you're interested in a fast cruise speed. The repowers that I'm familiar with on these boats included beefing up the stringers and increasing the size of the exhaust system, and reducing the reduction gears from the OEM 2.1 to around 1.5, which reduces the shaft torque and should allow a 1.5" shaft. The best way to harness the extra power over the OEM setup is to increase shaft rpm as the prop diameter can't be increased beyond the OEM 20".

There's some good documentation here on a repower of a M1 with a 315 hp Cummins.
https://mainship34.com/repower/

Looks like a nice project, but do your diligence...
Was that a 315hp Cummins or a 270?
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Old 01-27-2020, 06:54 PM   #15
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Was that a 315hp Cummins or a 270?
Just rechecked and it's 305 hp. My mistake.
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Old 01-28-2020, 07:48 AM   #16
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Quote:
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Was that a 315hp Cummins or a 270?
If you are referring to MY repower notes, it was a 270.
However, the 315 shares the same power curve up to 2600 rpm. The extra power is gained after that up to 3000 IIRC.

And yes changing to 1.5 reduction keeps the prop the same pitch, however the added shaft rpm makes fairing the keel and beefing up the hull above the prop necessary to eliminate the vibration.
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Old 01-28-2020, 09:02 AM   #17
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If you are referring to MY repower notes, it was a 270.
However, the 315 shares the same power curve up to 2600 rpm. The extra power is gained after that up to 3000 IIRC.

And yes changing to 1.5 reduction keeps the prop the same pitch, however the added shaft rpm makes fairing the keel and beefing up the hull above the prop necessary to eliminate the vibration.
"And yes changing to 1.5 reduction keeps the prop the same pitch, however the added shaft rpm makes fairing the keel and beefing up the hull above the prop necessary to eliminate the vibration."

Is it possible to achieve a 2X safety factor on that 1.5" shaft with 270 hp and, that prop and those shaft speeds?
Do you still retain at least a 10% spacing between the prop tips as compared to prop diameter or do you change prop diameter as well?
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Old 01-28-2020, 10:34 AM   #18
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Quote:
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"And yes changing to 1.5 reduction keeps the prop the same pitch, however the added shaft rpm makes fairing the keel and beefing up the hull above the prop necessary to eliminate the vibration."

Is it possible to achieve a 2X safety factor on that 1.5" shaft with 270 hp and, that prop and those shaft speeds?
Do you still retain at least a 10% spacing between the prop tips as compared to prop diameter or do you change prop diameter as well?
Yes I still had more than a 2x safety factor. Shaft was Aquamet 22 material. I should note that the 77 and 78 Mainships had a 1 1/2 inch shaft as oem. In 79 and beyond they changed to 1 3/8 and also increased the shaft angle to allow more clearance to the hull.
A 20 inch diameter prop still barely met the 10% rule of thumb. I kept my 20 x 21 prop. Same one I had for the 160 Perkins at 2.1:1 reduction. It worked out perfectly as my WOT was 2630 after the repower.

Regarding "safety factor".... 2x is good 3x is better but when I worked as an engineer we had a product that had a 1.1 safety factor and never had a field failure.
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Old 01-28-2020, 10:44 AM   #19
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Yes I still had more than a 2x safety factor. Shaft was Aquamet 22 material. I should note that the 77 and 78 Mainships had a 1 1/2 inch shaft as oem. In 79 and beyond they changed to 1 3/8 and also increased the shaft angle to allow more clearance to the hull.
A 20 inch diameter prop still barely met the 10% rule of thumb. I kept my 20 x 21 prop. Same one I had for the 160 Perkins at 2.1:1 reduction. It worked out perfectly as my WOT was 2630 after the repower.

Regarding "safety factor".... 2x is good 3x is better but when I worked as an engineer we had a product that had a 1.1 safety factor and never had a field failure.
Makes sense as our 1978 Mainship had a 1-1/2" shaft but was not Aq22 with the 165 Perkins and a 20" prop.

There were a bunch of these types of similar conversions done on the Bayliner 38 boats where the original engines were a pair of 175 HP and they swapped to various options in the 300-350 hp ranges. The shafts were 1-1/2 and the 'stock' props were very typically 21" or 22".
Some of those experienced shaft failures within a few years with the increased engine power - the calculated safety factor with them was lower than 2 but well above 1.
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Old 01-28-2020, 12:14 PM   #20
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OEM shafts were bronze on the Mainships. Aquamet is much stronger.
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