LM18 Houston Tx

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ericwensel
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Re: LM18 Houston Tx

Post by ericwensel »

I started the hunt for a motor today and found that getting motors right now may be a challenge. I talked with a Mercury dealer who said the current delivery is May 2022. He did say keep looking and I may find one.

One question he had is whether the boat had been USCG rated yet. It has not but I did some checking and per USCG, i am concerned that the boat may not be rated for the 40hp i had hoped. If anyone can check my assumptions, i would be greatful.

L = Boat Length = 18ft
W = Transom Width = 4.1ft (top of transom dimension)
Factor = F = LxW = 73.8
Transom Height is less than 20" hence use the following calculation
HP Rating = (0.5 X F) - 15 = 21.9

Mojosmantra
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Re: LM18 Houston Tx

Post by Mojosmantra »

I ran into the same thing with motors and it seemed like I wouldn't be able to get my hands on one until next year, but I continued to search and was able to find one fresh off the ship. So, it's possible. I will say that I did not get a deal on it.

jacquesmm
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Re: LM18 Houston Tx

Post by jacquesmm »

The USCG max. HP, number of persons and load capacity, buoyancy and upright flotation are required for production boats not for self built boats however, it is safer to stay within their parameters if only for insurance purpose.
The capacity tag calculations are more elaborate than what you show but a quick run through my spreadsheet shows, for a 20" shaft, max. 54 HP with remote steering
and 32 HP for a 15" shaft.
Per ABYC H26_5, the factor should be 72.
If it was a flat bottom, max. would be 21 HP, that is probably what you used.

Get a 20" shaft if you want 40 HP or a 30 HP if you use a 15" shaft.
A 20" shaft will require to cut the transom higher. I show how to do that here:
https://boatbuildercentral.com/support- ... ansoms.pdf

Your dealer is correct about motors availability. The situation is really bad in the whole recreation industry. Many factories closed or slowed down for the Covid crisis and we are not back up to speed, far from it.
Smaller engines that you can install yourself like a 30HP, are easier to get. A 30 will push that boat nicely, even a 25 will work well.
Jacques Mertens - Designer
http://boatbuildercentral.com

ericwensel
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Re: LM18 Houston Tx

Post by ericwensel »

That was very quick reply. I appreciate the response.
I did assume a transom height of <20" hence that is why I used the lesser calculation. As the transom is +20" at the center (but less than 20" at the sides) do you think i can use the 2xF-90 calc. I do plan on using 20" shaft.

TomW1
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Re: LM18 Houston Tx

Post by TomW1 »

.Yes the 2xF - 90 would be fine. I had just gone through using the USCG calculations when I saw Jacques had replied. They were almost identical. Are you doing tiller or console steering. If tiller, both the ABYC and USCG reduces the HP limit for a boat. Normally by 1/4. So 40 becomes 30. But they do not disallow a 40 it is just there recommendation. :D You could put a 100 on it but you might have a problem getting insurance. :lol:

One thing you always have to remember is that dealing with the USCG some of there Regulations are requirements and you can get fined for them and others are Regulations that they highly suggest.

As far as getting a motor goes, one of the members on here was told 3-4 months but had it in 4 weeks. Not the color he wanted, but at least a motor. I would say get your order in with every outboard dealer in close proximity to you and take the first one that comes in and cancel the rest. The motors these days are pretty much the same as far as quality and you won't go wrong whether you get a Yamaha, Honda, Suzuki or Mercury.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

ericwensel
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Re: LM18 Houston Tx

Post by ericwensel »

OK. Sounds like I can be comfortable with a 40hp. I like the Merc 3 cylinder as it is fairly light. As suggested, I will get it in order and hopefully when I am ready the motor will be here.

I hope to glass the cockpit this weekend. It is glued down. I also got the gas tank in this week. Not sure how I will secure. I have seen some set it on rubber pads. I like that approach. I am thinking I will set the bolts similar to what I have seen on Reid's FS18 build.

Image

Image

Image

TomW1
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Re: LM18 Houston Tx

Post by TomW1 »

Nice work going on there. And that is definitely a very nice tank. I had a way to secure a tank but my computer was hacked last month so have lost all my files It used strips instead of a solid pad. Let me see if I can find it. This guy was a marine surveyor. I found it, http://www.marinesurvey.com/yacht/fueltank.htm He explains why the system works.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

ericwensel
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Re: LM18 Houston Tx

Post by ericwensel »

More progress. Glassed the cockpit.

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Cbuf
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Re: LM18 Houston Tx

Post by Cbuf »

ericwensel wrote: Fri Jun 04, 2021 3:26 pm I started the hunt for a motor today and found that getting motors right now may be a challenge. I talked with a Mercury dealer who said the current delivery is May 2022. He did say keep looking and I may find one.

One question he had is whether the boat had been USCG rated yet. It has not but I did some checking and per USCG, i am concerned that the boat may not be rated for the 40hp i had hoped. If anyone can check my assumptions, i would be greatful.

L = Boat Length = 18ft
W = Transom Width = 4.1ft (top of transom dimension)
Factor = F = LxW = 73.8
Transom Height is less than 20" hence use the following calculation
HP Rating = (0.5 X F) - 15 = 21.9

I started with a 50 Hp tiller etec, I hated it. Once you have a hydraulic tiller(old boat) it is had to go back to non assist tillers. Then I cut it apart and added a console. The 50 is fine for the boat and I go about 34mph with a nice cruise at 28mph. My 2 cents is get the most HP in the frame/weight of the motor. For example the etec 20,25,30 are the same motor, the 40,50, and 60 are the same motor. The etec 60 while was the same weight they wanted like another 1000 for it. So like you I wanted a 40, but since a 50 cost 300 dollars more at the time, and was the same weight I got it instead. I went etec for the no maintenance, but had I gone 4 stroke I would have got the tohatsu as it was the lightest. A while back I put together a weight spreadsheet. At the time Merc didn't offer the big tiller handle with the smaller motors, and I hated the standard tiller handle because it was short, the fiction rings would wear out like every season, and shifter was way back on the handle. I think now they are offering the "Big tiller" handle on 30-60, so I would check into that. Remember just because you can extend the tiller handle, doesn't mean you can still reach the shifter.

This is from about 3-4 years ago, you might want to remake it with current offering. Additionally, the old 30 and 40 Yamaha 2 stroke were light and bullet proof. Had I found a 40 or 50 2 stroke yamaha, I probably would have bought that instead and save a bunch of money.


Cbuf.
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See my LM 18 build here.
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See my LM 18 Questions here.
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Finished Boat Here
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TomW1
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Re: LM18 Houston Tx

Post by TomW1 »

Yep Chuf there is not much difference in the 40HP weights. 20- 30 lbs will not make much difference in top speed, maybe 1-2 mph for a 40HP. Motor weight is a small part of the over all weight of the boat and load, less than a 1/4. :D

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

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