Dillon Laker 14/16.5 Wooden Tunnel Hull Build/Mod Project

[gomopar440]

I forgot to add the question that I had come up recently. I was reading some posts about selecting the right prop for your hull and motor combo in a thread here in iBoats, and a few links were offered to help the OP find the info he was looking for.

Here's the links BTW: http://www.go-fast.com/boat_speed_predictions.htm, and http://www.go-fast.com/Prop_Slip_Calculator.htm.

The boat hull I'm building, in it's original configuration, weighs 350lbs according to the designer. However I'm adding 2' to the overall length and almost 1' to the width. If I use the same factor (original dimension x 1.14) I used to up scale the dimensions, and apply that to the weight (350 x 1.14) that should give me a rough ballpark figure for my hull (= 399). I also plan on adding fiberglass to the outside to seal the wood so I'm guessing at least another 50lbs added on for that (399 + 50) to get an approximate hull weight of 449. The Tower of Power with the power tilt/trim weighs in at 315 and I weigh 215lbs So hull + motor + me should weigh in somewhere around 979lbs. I'll make it an even 1000 lbs to factor in a bit of fuel as well. When I go to that speed prediction link and punch in the figures I know, Weight = 1000; Prop HP = 115; Constant (fast catamaran is the closest match to the Laker) = 300; and then hit the [Calculate] button in the Speed column I get a speed of 102. Can that be right? Granted I haven't factored in prop slip or anything like that yet, but... Is this thing really going to be a triple digit boat?!?!?!:faint2:

BTW, the motor I'm using is a 1984 Mercury 115 HP inline 6. This was the first year the 115HP rating was measured at the prop shaft. Prior year 115's were actually crank shaft rated, so by the time it got through the gears and such, you had 5-10% less at the prop.

EDIT: Ok I used the second link to find the effect of the prop slip estimate (4-6%) on top speed. Gear ratio on my lower unit is 2:1 IIRC. For pitch I used 19 which is based on Arch's prop testing with Max and Miss Morgan. Max RPM for this motor is 5500. Theoretical speed from the first page is 102. With thos figures if I put in 4% prop slip I get 98 for the actual speed, and if I use 6% I get 96. Those slip corrected speeds are still WAY higher than I was expecting. I was telling my wife this is probably was going to be a 60-70MPH boat thinking I was probably only fibbing maybe a little bit. She already said she wouldn't ride with me in it at those speeds. It looks like I might have to build this boat in the single seat configuration instead of the two seat setup.:facepalm::laugh:

 

[gm280]

gomopar440, I will predict you will never ever get that boat going anywhere close to 90 MPH. I say high 50's low 60's is going to be it. I had a high performance Bass Boat, a Glasstream HydroBass with an inline Mercury 6 with a 21 pitch SS prop with adjustable tilt and trim and Jack plate and it turned 63 or close 65 on select water. So there is no way to get 90 MPH from your setup, and that is a guaranty. JMHO

 

[Patfromny]

Fastest boat I was ever in was I think a 17 ft Tahiti with an evinrude 235 on it with work done to the motor. It went around 90. I think gm's figure is closer than the prop calc. Still. 60 feels like 120 on the water. Nothing to sneeze at. Get used to boating alone whichever way it turns out. The Tahiti was stupid, about 4 inches of free board at around 70 (the boat was new to him and that was as fast as he was comfortable going at the time) was way faster than I would ever want to go. Only rode in it once. That was enough for me. I have a buddy who builds race engines who built two high hp big blocks for his friend with some type of cigarette boat that is in the 100 mph range. I think it takes a whole lot of stink to get to 100. I am by no means an expert in this area though. I'm struggling big time to get my little boat to 30.

 

[archbuilder]

Gomopar, I think that your wife will ride with you! I have a 19 pitch on Miss Morgan. My guess is she is around the same weight as your build. I get about 50 (GPS) out of her trimmed out on flat water. It takes a lot of horsepower to weight ratio to get to 100. My friend's Skater will do 120, but that thing is more like an airplane than a boat! I think you would actually have to change the gear ratio on a TOP to go that fast, assuming the motor could turn a ratio that high, given the load. This calculator seems to be a little more realistic to me.....but it would be cool if you went 100
http://www.csgnetwork.com/marinepropcalc.html

 

[archbuilder]

by the way, do you have any pics of the boat design you are building? I'm kind of curious what she is going to look like.

 

[Patfromny]

I tried that calculator arch posted and it says that the mph verse pitch is a negative value for slip. It did that for both props and speeds my boat has acheived. Weird. It says the rpm and pitch cannot make that speed...even though they did on my boat. Maybe I'm doing something wrong here. I first put in 13 pitch 2.67 gear ratio 6000 rpm and 28.3. Then a 15 pitch, 2.67 ratio, an 30.4. At 5200 Both gave me a negative slip reading. Those are GPS mph and was using the evinrude program on a laptop for rpm. No provision for hp or boat weight though so a weird calculator.

 

[archbuilder]

Pat, I plugged in Miss Morgans vitals and it got close, but I did get a negative 1% slip too. I tried the one gomopar posted....and she should do 85, lol I wish!

 

[shaw520]

Mopar,.. this looks like its going to a fun build, my first boat was a mid 70's Silver Line (I believe 17ft) with a 1982 Merc 115. Boat was rated for a 75hp, not sure how fast it would go as this was well before gps, and the speedo never worked!. But it scared the bygeezus out of me and some friends a couple times,... one of them would never get on board again!

I dont have alot to offer you in terms of build help,... but I will tell you this,.. Ive seen more than one Merc 115 (mine) get toasted due to one lean carb, with (3) carbs feeding 6 cylinders, you wont always notice a lean condition in one carb, specifically the middle carb. That lean condition will toast either one or both of those cylinders in short time. So its important to sync the carbs and do regular plug checks to make sure.
Cheers and good luck with your build

 

[gm280]

Pat, I plugged in Miss Morgans vitals and it got close, but I did get a negative 1% slip too. I tried the one gomopar posted....and she should do 85, lol I wish!

Arch, you know and I as well know he is never going to see 85 MPH ever. HP and boat speed are similar to so many other issues. Bell curves prove that over and over again. You gain a lot more speed verses HP initially. But it take double, triple or quadruple or more HP to gain a minute amount of addition speed. Look at any drag racer. Same as sound volume. Easy to get a decent DB volume with a few watts of power. But extremely hard to get increased DB gain even with huge amounts of wattage power. Math and reality work that way. JMHO

 

[archbuilder]

Gomopar, sorry if GM and I are hijacking! I will be really interested to see what she runs when you get her together. Wish I was closer, I might come pick up a free boat:bounce: yeah just what I need!

 

[gm280]

:sorry: Gomopar. I honestly didn't mean to hijack your thread, I certainly do apologizes as well. :brick:

:focus:

 

[Patfromny]

I don't think you're hijacking. He didn't even believe the 100 mph estimate. I think 60ish is a good conservative number. Anything more I would consider gravy. I can speak from my own experience saying that 60 is absolutely flying on the water. No need for anymore. It sure was dangerous feeling not being at the wheel too.

 

[shaw520]

Deleted,

 

[gomopar440]

Gomopar, sorry if GM and I are hijacking! I will be really interested to see what she runs when you get her together. Wish I was closer, I might come pick up a free boat:bounce: yeah just what I need!

Seriously guys, don't worry about the hijack, I did the same over on Arch's Fuggly build before I started this thread. It's all related info pouring in here so it's all good. Speaking of pouring, it's pouring out here with thunder and lightning right now too, so I'm not going outside to work on the boats in that mess until it lets up. And as far as coming to get the boats go, take two they're small. :laugh:

I posted the data I found from that calculator because I was surprised to see it give an estimate that high. To be honest I find it hard to believe that it will get anywhere close to that speed. Bob Dillon (boat designer) built his Laker as per the plans he drew up as a single seater and was getting right around 60MPH with a '78 Merc 70HP motor (as of Oct '14). It looks like he hasn't posted any performance updates on the website since he got it running though. I read elsewhere he's made some prop and jackplate changes and was getting closer to being happy with the setup, but how much I don't know. I'll email him and ask him about the current performance figures on his Laker as post back here with what he says.

Pics of the Laker and basic performance data can be found at this link: http://www.dillon-racing.com/Laker14/plans.htm
However, I'm working on a copy of the hull outline in MS Paint to try to come up with a paint scheme for it. I'll post it here when I get done with it. The line drawing (as well as some completed pics) can be see in it's unmodified form on the page in that link.

I'll try the other speed estimator link posted above let you guys know what I find out on this other speed calculator/estimator. Keep in mind this is all just rough ballpark figures at this moment. Well, except for my weight, that's pretty accurate right now. The motor weight should be pretty close as well since I got from the Mercury Factory Service Manual for my motor and I also confirmed it on the NADA Guides website. I'd like to actually weigh it if I can find a scale that will accurately read that high. I need to pick up a heavy duty scale (660lbs max) to set up my sand rail suspension, so maybe I'll bump it up on the priority list. They can be found on Ebay for around $50-60 if you look around long enough.

BTW: I emailed the people running that speed calculator I posted a link to in order to find out if that number is supposed to be MPH or KTS. It doesn't say one way or the other from what I could see and just calls that figure "Speed". The automated response I got when I sent in that question said they would reply back during normal working hours. So I don't expect a reply from them until sometime next week at the earliest.

 

[gomopar440]

I wanted to mention one of my ideas about this build that I don't think I've covered yet. I'm shooting for sort of a retro look with this boat build rather than a modern look. The overall shape of the Tower of Power fits in great with that idea IMHO, but the squarish front cowling cover just doesn't seem to match. I lucked out and found one of the older looking front covers in the bottom of the green Larson hull I got, so I'll be using that one instead of the original one. It looks like it'll fit perfect once I get the front latch on the upper cowl piece replaced (it's missing). I'll be doing a set of custom decals for the ToP so making the old cover look like it belongs there shouldn't be a problem.

Here's a pic of the two front covers side by side to get a better idea of what I'm talking about.

I'm still working on the Paint drawing of the boat, but this is where I'm at with it so far.

 

[sphelps]

I agree the old style motor plate does look better .. Looking forward to seeing what paint scheme ya come up with ...
Btw, With a user name like yours just wondering what ya got stored in the garage ... An old Hemi Cuda or something maybe ?

 

[gomopar440]

I've been using the user name "GoMopar440" for well over a decade on all the forums I sign up on. I've have Challengers, Chargers, Power Wagons, etc. Most of them started out with 318's, but ended up converted over to 440's by the time I was done with them. The '70-74 Challengers are still my favorites. Unfortunately, the only Mopar we have left is the wife's '02 Grand Cherokee. I'm always keeping an eye out for an old M37 that I can swap in a 12V Cummins and 1-ton truck drive train into.

 

[gm280]

I've been using the user name "GoMopar440" for well over a decade on all the forums I sign up on. I've have Challengers, Chargers, Power Wagons, etc. Most of them started out with 318's, but ended up converted over to 440's by the time I was done with them. The '70-74 Challengers are still my favorites. Unfortunately, the only Mopar we have left is the wife's '02 Grand Cherokee. I'm always keeping an eye out for an old M37 that I can swap in a 12V Cummins and 1-ton truck drive train into.

I once owned a new show room '72 Challenger with the 340 thermoquad. While not a 440 or 426 Hemi, it was a lot of fun driving. Wish I still owned it too.

 

[archbuilder]

I like the old face plates too. I stuck with the 80's one and changed the graphics to the blue scheme, which is a great improvement....brown, really lol! Thanks for the drawing, this is going to be a cool build!

 

[sphelps]

I think having just a 70 Duster with a 318 would be cool ! My brother had one years ago now he has Ply Belvedere 60 something convertible ..