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Old 03-25-2017, 03:17 PM   #1
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Another 40 ft Mainship twin vs single question

To the Mainship experts...

I've been told that the 400 Mainship single drafts more than the twin... by as much as 8 inches or better. Is this correct?

Also, I've been told that it really doesn't make a lot of difference in that the singe engine is prop is better protected by the keel where the twin is not. Issues?

I do prefer a shallower draft boat, for the most part.
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Old 03-27-2017, 01:11 PM   #2
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No experts on the Mainships?
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Old 03-27-2017, 01:48 PM   #3
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To the Mainship experts...

I've been told that the 400 Mainship single drafts more than the twin... by as much as 8 inches or better. Is this correct?
True, Think of the hull somewhat like a wine glass. by spacing the shafts out to port and stbd on a twin, they are higher up the hull than a single. This applies to all boats. Even your express cruiser would have a deeper draft with a single I/O than with twins.

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Also, I've been told that it really doesn't make a lot of difference in that the singe engine is prop is better protected by the keel where the twin is not. Issues?
The larger singles have a shoe that extends beyond the keel and protects the prop and rudder. Twins do not have this. So when running aground with a twin, you'll be hitting the props and rudder

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I do prefer a shallower draft boat, for the most part.
8 inches is not significant. Stay away from skinny water.
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Old 03-27-2017, 10:36 PM   #4
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True, Think of the hull somewhat like a wine glass. by spacing the shafts out to port and stbd on a twin, they are higher up the hull than a single. This applies to all boats. Even your express cruiser would have a deeper draft with a single I/O than with twins.



The larger singles have a shoe that extends beyond the keel and protects the prop and rudder. Twins do not have this. So when running aground with a twin, you'll be hitting the props and rudder



8 inches is not significant. Stay away from skinny water.
8 inches for me is huge, not small. I can put this boat behind my house and with a 3 foot 3 inch draft i could get it out 98% of the time.....

If it were 3 ft 8 inches (the specs I see on the 40 Mainship), I'd get out perhaps 80% of the time which is a huge difference.
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Old 03-28-2017, 02:11 AM   #5
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That's only 5 inches difference. Are you in a tidal area? If so, what is the MLW?
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Old 03-28-2017, 02:16 AM   #6
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8" difference in draft on a 40' boat ? me thinks u need a different boat
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Old 03-28-2017, 08:22 AM   #7
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I like singles, but don't want to start a singles vs twin argument.

I cruise on the ICW Southeast VA and NC, not uncommon to have a log roll under the hull on some of our waterways. I have seen the entire running gear on the port side of a Grand Banks last year damaged by a log.

I owned a Mainship 390 with single Yanmar about 10 years ago and loved it.

If I had the choice, I would choose the single. But that is me.
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Old 03-28-2017, 09:08 AM   #8
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How quickly does the water depth drop in front of your slip? In most areas, soft silt builds up in the slip and after using the slip for a while a slight trench develops that deepens it. The slip where you see my boat in the avatar to the right is at least a foot deeper in the middle.

Or with judicious use of lines tied between the boat and dock you can run your engine up for a few minutes and easily blow the silt out and get another 8" water depth.

I used my boat (just before pulling the prop for tuning) to blast out a 50' trench into my neighbors slip so he could get his sailboat in and out more easily.

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Old 03-28-2017, 01:23 PM   #9
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That's only 5 inches difference. Are you in a tidal area? If so, what is the MLW?
Yes, tidal area on the inter coastal in St. Pete, FL. MLW is .33, but not sure what that means to me. The tide swing is ~2 to 3 feet, with some pretty shallow lows in the winter.
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Old 03-28-2017, 01:54 PM   #10
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I apologize for not being clear. (MLW = Mean Low Water) which should be the average depth on a chart at low tide. I'm looking for the average depth at low tide for your dock (and approach).

.33 would be the height (in Feet) of the tide above MLW for that specific day for that specific low tide (2 lows per day). That means on that tide cycle, that low tide is .33 ft above normal.

The height of the high and low will vary from day to day. Some low tides are negative numbers, some are positive. (all high tides are positive numbers because they are based on the height above MLW). Last Sat. your area was -0.2 at Low. (roughly 2.4 inches lower than the normal low tide).

This kind of brings me to the point where I would personally be concerned. You're tide is already going to swing from 2-3 inches below normal low and above the normal low. If we're slicing and dicing 5-8 inches of draft (where the low tide already varies 4-6+ inches from tide to tide, then that would be too shallow for my comfort level.
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Old 03-28-2017, 02:13 PM   #11
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I'm sure its coming however.........

Can anyone clarify if I'm using MLW properly??
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Old 03-28-2017, 02:29 PM   #12
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How quickly does the water depth drop in front of your slip? In most areas, soft silt builds up in the slip and after using the slip for a while a slight trench develops that deepens it. The slip where you see my boat in the avatar to the right is at least a foot deeper in the middle.

Or with judicious use of lines tied between the boat and dock you can run your engine up for a few minutes and easily blow the silt out and get another 8" water depth.

I used my boat (just before pulling the prop for tuning) to blast out a 50' trench into my neighbors slip so he could get his sailboat in and out more easily.

David
David,

Water drops from high to low in about 6 hours.

Yes, there's a lot of silt, and can move some of that away. The boat will be docked to the right of the walk way, which gets shallow pretty quick, mostly muck. But running out that channel has a few low spots that are about 2.5 feet at low tide. Fortunately it's all muck, no rocks, so I suppose with a lot of use it would get easier.

Also turning around will be dicey, and impossible at low tide.

The benefit of having the boat close by includes the inconvenience of not getting out sometimes. I've got a few easy back up places where I could dock overnight or for a few days on those times where departing on time could get done.

I'm just guessing that 8" could improve my departure time from 75% to 90%.... and also arrival issues.

So, I'm not rethinking the twins, leaning toward them.


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Old 03-28-2017, 02:56 PM   #13
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I'm sure its coming however.........

Can anyone clarify if I'm using MLW properly??
Shrew, I have no clue. As I understand it, the MLW is the average low tide, and mine at .33 is .33 feet above the zero line which I believe is sea level, which shows up pretty clear on tide prediction charts.

However, it has to be seasonal, as today at my .33 I could out with little effort. When it's low in the winter, the low swings will go to maybe a foot below the zero line.

Below is extreme low, happens perhaps every other year, but would close operations down. The trawler's bow would be in the mud other side of the lift. However, if that Sundance was not on the lift I could get it out but would kick up some mud.





Overall, I think things will work fine, but certainly want all the advantages I can get.
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Old 03-28-2017, 02:57 PM   #14
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Shrew,

Another thing... it's not about what the tide is or isn't... it's how deep the water is.
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Old 03-28-2017, 03:23 PM   #15
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Just wait a few years. Global warming will melt some more of the polar caps and raise the water level ;-).

But seriously, I'll bet you can deepen your slip and approach with a bit of judicious prop wash so you can get in or out 95% of the time. Yes, you may have to nose bow in when the tide is low and come back a few hours later at high tide and turn it around.

We dealt with this all the time in the shallow creeks of Oriental, NC when I lived there.

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Old 03-28-2017, 03:37 PM   #16
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8 inches equals 200 more rpm on departure unless you slip is bedrock.

Plus daily and seasonal variations are often more a factor than astronomical predictions.
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Old 03-28-2017, 05:59 PM   #17
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Shrew,

Another thing... it's not about what the tide is or isn't... it's how deep the water is.
I agree. That is essentially the question I was trying to ask (admittedly poorly).

How deep is the water on average at low tide?

Is that your dock and lift? (I ask only because it isn't the 280 Sundancer in your signature) Can it be dredged?
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Old 03-28-2017, 08:13 PM   #18
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I'm sure its coming however.........

Can anyone clarify if I'm using MLW properly??


MLLW - mean lower low water. That is the datum that tides are referenced against. I found this - https://tidesandcurrents.noaa.gov/datum_options.html.

I think this is the mean of all the lower of the two low tides each day, as opposed to MLW which includes the "other" low tide point each day in the mean calculation. I think.
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Old 03-28-2017, 09:40 PM   #19
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I agree. That is essentially the question I was trying to ask (admittedly poorly).

How deep is the water on average at low tide?

Is that your dock and lift? (I ask only because it isn't the 280 Sundancer in your signature) Can it be dredged?
Shrew,

Yes, that's my dock and the Mainship will be docked outside of the Sundancer. And yes, it can be dredged, which I'll probably do in the dock area, as just turning it around will have challenges. However dredging down the canal is not an option.

But might be better that I though.... I floated the length of the canal tonight at MLW, and measured at every 10 feet or so, and a bit deeper than I thought, but a few spots at 3 feet. I bet I could get thru that, but would kick up a lot of mud. Is that a big issue with the impeller? Suspect it would, so if easy to change, would be a non issue.

Here's the other pic I was trying to post with extreme low tides, which happen about every other year. The bow of the Mainship would be just the other side of the lift.....

[/URL][/IMG]
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Old 03-29-2017, 03:15 PM   #20
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Hey SeeVee,

As far as draft goes, in many places, like the PNW or perhaps Australia (I've never been there so I don't know) 5 inches or even 8 inches doesn't matter. On the gulf coast of Florida 5 inches makes a ton of difference. I wouldn't want to blow mud out of the canal everytime I left at low tide. You never know what's under that mud and I can tell you from experience bent props are pretty expensive to fix.

Here is a post I made some time ago regarding the MS400 T with Twins (my boat) vs. with a single.

I don't want to start up the too long running twins vs. single debate but I own a 2005 400T with twin Yanmar 4lha-stp 240 hp and looked long and hard at single vs twin IN THIS SPECIFIC BOAT before I made a decision. Sorry for the caps, but I want to be clear that I am speaking of the Mainship 400 and only the Mainship 400 here.

Unless fuel economy is your primary concern to the point where a very small difference will swing it for you the twin is a better boat. The single has two advantages, the aforementioned minor difference in fuel economy and a lower purchase price though this is off set by a higher resale value for the twin.

Our boat runs comfortably at 15 knots at 2800 RPM, sometimes a hair faster sometimes a little slower depending on sea state and load. I've put about 200 hours on my motors at that speed and have been tracking my fuel burn. It burns right at 13 GPH, so 1.15 MPG. At 1700 RPM I run at hull speed, right at 8 knots, again give or take according to conditions, and burn 3.75 to 4 GPH, or 2.13 MPG. Over a month long cruise, a mix of hull speed and fast cruise, I always end up burning 10 GPH including genset use.

The specs I've seen on the single have it burning pretty much the same at hull speed, but it really jumps up at higher speeds. I suspect that the boat doesn't start to flatten out unless you really push it with the single. With tabs down my boat flattens at about 13 knots.

The single just isn't made to run faster than 8 knots, which is OK I guess if that is all you ever want to do. But for me the ability to go faster when I want to is a huge advantage that far offsets the tiny difference in fuel burn.

Think of it this way: It's 110 NM from our home port in Stuart, FL across the stream to Grand Cay Bahamas where we usually clear in. If I ran it the entire way at hull speed we burn 51.6 gallons and it takes us 14 hours. If we run at fast cruise we burn 95 gallons and it takes 7.5 hours. In the single, assuming a fuel burn of 3.5 GPH, that's 48.24 gallons and 14 hours.

So if you are in a single and go slow (really your only choice) it costs you $145.

If you are in a twin and go slow it costs you $154.

In a twin and go fast $285.

The single saves you nine bucks. One and half Kalicks in the Bahamas.

Or, if you choose in the twin you can spend $150 more and get there in half the time.

If it's rough and your wife gets tired of slogging around on the banks you can bump it up, bang through the chop instead of rolling and keep her happier.

Some other advantages of the twin in the 400T: They draw less water. You have a get home motor. You don't need a thruster, which aren't free and are one more system you need to maintain. From an engine access standpoint the twin has some advantages and the single has some; pretty much a wash.

Overall, for a Mainship 400, the twin is the way to go.

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