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Old 03-30-2019, 04:54 PM   #1
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Cool Modifying a fly bridge Searay to pretend itís a trawler

Just a fun idea to kick around, considering taking a 30í Searay flybridge and tearing out the 350 Cu Inch inboards, plugging the holes, removing the shafts props and rudders and installing two transom sea drive mounts with 50-75 HP outboards.

Here is the questions how much ballast would need to go in to offset the engine removal?

How fast could it go with 100-150HP?

How much would be estimated fuel burn at hull speed 6-7knots?
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Old 03-30-2019, 05:19 PM   #2
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Are you doing this for fun or to save a few bucks?

If the former, then go for it! Could be a fun build.

If the latter, then run away. Fast!
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Old 03-30-2019, 05:23 PM   #3
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Something like this ?
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Old 03-30-2019, 05:47 PM   #4
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Originally Posted by tracyt View Post
Just a fun idea to kick around, considering taking a 30í Searay flybridge and tearing out the 350 Cu Inch inboards, plugging the holes, removing the shafts props and rudders and installing two transom sea drive mounts with 50-75 HP outboards.

Here is the questions how much ballast would need to go in to offset the engine removal?

How fast could it go with 100-150HP?

How much would be estimated fuel burn at hull speed 6-7knots?

Would work fine as a river boat and i've seen plenty of homemade boats do the loop that would be much worse.

I'd skip the "seadrive mounts" and use an outboard bracket and a single outboard.

How fast you want to go would depend on how much power you hang on the back. I would personally go with a 150hp optimax or a similar direct injected outboard that will use very little fuel at trawler speeds. A single 150 might plane a 30' searay in good conditions but a 250 would for sure. I wouldn't bother with twin engines.

Bertram 28'ers have been done this way if you're looking for inspiration.
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Old 03-31-2019, 06:34 AM   #5
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Quote:
Originally Posted by tracyt View Post
Just a fun idea to kick around, considering taking a 30í Searay flybridge and tearing out the 350 Cu Inch inboards, plugging the holes, removing the shafts props and rudders and installing two transom sea drive mounts with 50-75 HP outboards.

I suspect you'd be starting with a $50K (example, ??) boat, spending $25K (??) on the refit, ending up with a $20K (??) boat.

Compare potential expensive refit costs to doing nothing but driving slow. IOW, whatever you'd save in fuel just by running the existing engines at "trawler" speeds.

Your hull form won't necessarily be comfortable at slow speeds in all sea states... but then with existing power, as is, you could get up and go when it gets too sloppy for comfort.

-Chris
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Old 03-31-2019, 09:17 AM   #6
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I suspect you'd be starting with a $50K (example, ??) boat, spending $25K (??) on the refit, ending up with a $20K (??) boat.

Compare potential expensive refit costs to doing nothing but driving slow. IOW, whatever you'd save in fuel just by running the existing engines at "trawler" speeds.

Your hull form won't necessarily be comfortable at slow speeds in all sea states... but then with existing power, as is, you could get up and go when it gets too sloppy for comfort.

-Chris

I could find a 30' Sea Ray Gasser for under 10k or one that needs engines for under 4k(there's a clean one @ my dock for 8k), put a $3000 outboard(150 optimax) on a $700 outboard mount. I understand what you're saying but those are some big numbers.

I think the OP was asking about a boat that needed an engine or at least that's what it sounds like and IMO the only case where I'd consider an outboard.. Id rather run a twin engine boat without a second prop on one engine before i'd do that.


To the OP also check out Chris Craft if you're serious about moving forward with this. They are better built IMO.

I would recommend buying a boat boat with a single 350 in the 26-28' range(Trojan F26 or f28 are decent) and either reprop for trawler speeds or use as is. I looked at a F26 with a crusader for around 5k a while back. got about 2nmpg @ 20 knots and would get respectable mileage @ trawler speeds. Just too small for my needs.

Not quite what you were looking for but would save you tons of time, money and effort for a similar result but the outboard route isn't hopeless either.
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Old 03-31-2019, 09:18 AM   #7
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To the OP, I suspect it would be a big waste of both time and money, because in the end, you likely would not be happy with the results.


I have seen several instances on line, where folks have pulled a single I/O, glassed the hole, installed a bracket, installed an outboard, and seem to be happy with the result.


Aside from trying to rebalance the boat, my guess is that handling also would not be so great.


Jim


p.s. If you do, however, go ahead with the project, please post pics as I love a good build thread!
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Old 03-31-2019, 04:49 PM   #8
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Something like this ?


Thatís the new Northern Marine build isnít it?
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Old 03-31-2019, 05:27 PM   #9
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If the SeaRay had twin 454s, they could be replaced with a pair of 250/300 hp outboards on an Armstrong bracket. It would not have to float all the weight of the engines since you would be removing the gassers and their gears. Imagine how useful the old engine room would be for storage! You would also be removing all the underwater gear so it should plane easier and run faster.

I’d love to see how this worked out for SOMEONE ELSE.
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Old 03-31-2019, 05:49 PM   #10
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Greetings,
One has to consider that it is not simply take out the old inboards/I-O's , slap on a bracket and put on outboard(s). The transom was never designed structurally to take the load of hanging 150+HP on it. I suspect one would have to reinforce said transom in a large way.
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Old 03-31-2019, 06:23 PM   #11
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Quote:
Originally Posted by tracyt View Post
Just a fun idea to kick around, considering taking a 30í Searay flybridge and tearing out the 350 Cu Inch inboards, plugging the holes, removing the shafts props and rudders and installing two transom sea drive mounts with 50-75 HP outboards.

Here is the questions how much ballast would need to go in to offset the engine removal?

How fast could it go with 100-150HP?

How much would be estimated fuel burn at hull speed 6-7knots?

1) Ballast? Probably some but maybe none. You are moving the weight aft, so it may balance out. In the end, you would need to try it out and adjust as needed, no one here can tell you definitively.


2) How fast? Not very fast at all. This boat is a planing hull and it was designed for and built with 2 x 5.7 litre V8s (500-600hp). It needs them. 100-150hp will not get you up on plane, and the best you will ever do is plow up a monstrous wake. Or, go VERY slow.



3) Why do this? A de-powered planing hull will be a miserable ride. Are the current engines totally shot?



4) Trying to save on fuel by using smaller engines? Won't happen. At any given speed, that hull will burn the same GPH with large engines or small engines. Stick with the existing engines and slow down, you will enjoy all of the benefits of going slower without spending money through the nose.
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Old 03-31-2019, 06:30 PM   #12
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Perfect answer...
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Old 03-31-2019, 07:19 PM   #13
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If the SeaRay has V drives there should be no CG problem at all.
If straight drives moving fuel tanks fwd should do the trick.

As to speed the OB boat could be faster due to being lighter .. but not due the small outboards.
But outboards are heavy these days and the inbd may have bigger props.

But the underpowered SeaRay would suffer very significantly from her much shorter WLL. To cruise as a trawler the boat would be slow. Going as fast as a typical trawler the SeaRay would be constantly too high on her wave and require much more power.

Also the SeaRay being a planing hull is designed to go fast, get there and ... whatever. But on a trawler much more time will be spent underway and even more than that due to her lower hull speed. Will the SeaRay be comfortable w all that time underway?
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Old 04-01-2019, 05:55 AM   #14
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If the engines are shot, a modern engine , like a 4 cylinder with turbo , will weigh less than old anchor block engines and have the low speed fuel burn you desire .


Probably with enough power to not scare the next owner to thinking its a barge.
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