Bob's Geronimo - 2nd time

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bobinpowayca
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Bob's Geronimo - 2nd time

Postby bobinpowayca » Fri Apr 27, 2018 10:46 am

Howdy, we took her out again yesterday. The first time I couldn't keep the nose down or trim it right and I thought it was because there were too many people in the boat. So this time, just me and my wife and I was hoping for a smooth ride. We started out at the south end of San Diego Bay. We had a small headwind about 5-10mph, and a little chop on the water but not enough for whitecaps. And periodic waves from big boats.
So the problem was, the nose is too high. Most of the time I had to lean and look around the nose of the boat to see ahead. We were travelling 5-10mph, with the motor fully down. I tried to speed up to bring it "up on plane" but the ride was pretty rough. I expected it to nose down a little as I sped up to plane - I did get up to about 15 mph - i thought maybe this would be on plane and I started to raise the motor, but then it really nosed up. And I heard the motor whine sometimes - cavitation? I also heard this whine as I went over rollers.
On the way back down the bay, we had a tail wind. I still kept the motor all the way down. This time it was smoother, the nose was down better, and we were travelling about 20mph without realizing it.
Also, sitting empty at the pier she looked somewhat nose high. So here's some things to consider - I have 2 batteries, a full 14 gallon tank, and a 320 lb motor. Were those typical for a boat like this back in the 50's when Glen designed it? Also - the nose is just an empty cone - but when I built the motorbox, I tend to "overbuild". I framed it all out with white oak of larger dimension than plans, etc.
Oh yeah,another thought - this is a "high freeboard" design, which I thought would be good for going out in the ocean a little. But with the high freeboard, especially with the nose up, it's like a sail in the wind.
So here's what I'm thinking of doing. I don't want to put lead or steel weights, sand, etc up front because that would defeat my efforts to make the boat buoyant. I first thought of a large water tank like a bow tank, because you could add or siphon out water to get the weight right. But then there'd be the "slosh factor" if the tanks weren't full and that would really mess with the nose. So I'm going to get some 5gallon buckets with lids and bungs, and fill them full. Then belt them to the stem up in the bow. Maybe start out with 2 buckets (>80lbs). Doesn't seem like much weight but then it's at the end of the bow. Then find a calm lake and see what happens. Any thoughts? Thanks, Bob
Bob
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Built the Glen-L 17 (1988), Geronimo (2018)
PBR support (1968)

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chugalug
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Re: Bob's Geronimo - 2nd time

Postby chugalug » Fri Apr 27, 2018 11:53 am

:D does your motor have this rod across?mine is all the way in-might have to change later.its so motor can tilt forward.also any weight up front might help.
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BayouBengal
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Re: Bob's Geronimo - 2nd time

Postby BayouBengal » Fri Apr 27, 2018 12:38 pm

First, follow chug's advice to ensure that you're actually trimming the motor all the way in because after doing this, you may not need to do anything else.

Second, you could go with your five gallon bucket idea to figure out if the weight fixes the issue, but you might find it easier to work with weight lifting discs, or sand bags.

Third, you might need (or want) smart tabs. My first boat, a Squirt would not plane until I was up to about 15 mph and would quickly fall off plane when I slowed down. Initially, I felt putting smart tabs on it as a sign that I didn't build it very well. But honestly, the boat just rode so much better with them. Essentially, the boat went from difficult to plane to always being on plane even at very low speeds. My second boat has plenty of engine to plane and rode great until I added a swimdeck to the back, then it started to porpoise in the low 30's; so I added smart tabs to it also. After adding the smart tabs, it wouldn't porpoise until around 40 mph. Since then, I've also added 60 pounds of weight in the bow, and it now only porpoises with the boat running in the 40's with passengers in back. In brief, I think weight in the bow might solve your problem, but from my perspective, the smart tabs truly make the ride much much better and I'd pretty much use them now even if I didn't have an issue with porpoising or planing.

The ticket to having a great ride with your Geronimo can probably be found with a combination of bow weight and smart tabs.

PeterG
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Re: Bob's Geronimo - 2nd time

Postby PeterG » Fri Apr 27, 2018 1:11 pm

Some thoughts about weight and balance with this classic design...

The designer's assumptions would have taken into account the outboards and typical setups of the day. Those outboards for the most part weighed quite a bit less than modern ones, for example 250-275 lbs for a larger Mercury (65 hp and up) and a typical setup probably had just one starter battery and one or two 6 gallon fuel tanks. A full 6 gallon tank weighs about 36 lbs plus the tank, figure 42 lbs. Plus a typical 12V starter battery at about 40 lbs. That makes a design figure of about 332-357 lbs, all in the back end of the boat. Based on your setup with the 14 gallon tank, (about 90 lbs) two batteries (about 80 lbs) and motor (320 lbs) you have 490 lbs in the back end. That's 133 to 158 lbs more than the designer probably expected. These are rough numbers but they give a good comparison.
What to do? You can try an experiment: reduce the rear weight of your boat by reducing the fuel level to about a half tank and removing the second battery (of the two, keep the starter battery). That should shave about 95 lbs off the rearward weight and you can then see what effect that has on your boat's performance.
Adding ballast (weight) to the bow can correct the trim problems you are having, but overall your boat becomes that much heavier, which means slower to plane off, slower top speed and less fuel efficiency.

Keep us in the loop on your progress and most of all... have fun!
Murphy's Law: Anything that can go wrong, will go wrong.
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Bill Edmundson
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Re: Bob's Geronimo - 2nd time

Postby Bill Edmundson » Fri Apr 27, 2018 3:34 pm

Bob

I would try weight distribution first. I don't like moving the tanks. They are constantly changing weight. Some people have had luck with wedges on the bottom edge of the transom. Then there are Smart Tabs that are spring loaded. Then power tabs.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
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hoodman
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Re: Bob's Geronimo - 2nd time

Postby hoodman » Sat Apr 28, 2018 1:47 pm

Bob, maybe try sending Kirk Bellamy a PM on here: memberlist.php?mode=viewprofile&u=43906

He built a Geronimo over 10 years ago and might have some insight.

I think your experience of the boat hitting about 20 mph and then leveling out sounds about right. At 5-10 mph in a planing hull your just plowing through the water and pushing the bow up.

Also, the motor "whining" I'm sure is cavitation. There are a lot of prop gurus on here that might know better but maybe a 4 blade prop would help?

Hercdrvr
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Re: Bob's Geronimo - 2nd time

Postby Hercdrvr » Sat Apr 28, 2018 3:23 pm

I’d like to see a picture of his boat on the trailer with the engine trimmed in..... where the vent plate is ....and the angle of the transom. Something ain’t adding up here.
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hoodman
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Re: Bob's Geronimo - 2nd time

Postby hoodman » Sat Apr 28, 2018 4:07 pm

I agree, Matt, especially since we've seen 90 Etecs on Malahinis with good results.

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mrintense
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Re: Bob's Geronimo - 2nd time

Postby mrintense » Sat Apr 28, 2018 5:21 pm

Thanks for giving us an update Bob. Would it be too difficult to move the batteries forward?. Might help you get over the post build depression! :D :D
Carl
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bobinpowayca
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Re: Bob's Geronimo - 2nd time

Postby bobinpowayca » Sat Apr 28, 2018 6:28 pm

Okay Matt and MattB, here's some side shots of the boat.. There are no adjusting pins, those holes are just there. The only tilt adjustment is the trim switch on the throttle handle, and the tilting switch on the side of the motor. What you see here is the fully down position, i.e., I tilted it fully down until the servo squeaked. And the transom is 13 degrees to the keel.
Today I checked out a nearby reservoir that looked pretty calm. So Monday I'm going to take it there (I'm retired). This time I put some weight right up in the nose - a 35lb weight plate, a 25lb plate, and a 5gallon can of water, secured to the stem a rope and eyehook. Kind of like a big birthday cake. We'll see, I'll take a picture of her sitting at the dock so you can see how she floats. Thanks a lot folks for your advice. Bob
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Bob
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Built the Glen-L 17 (1988), Geronimo (2018)
PBR support (1968)

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chugalug
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Re: Bob's Geronimo - 2nd time

Postby chugalug » Sat Apr 28, 2018 7:08 pm

:D maybe good anchor could sit up front too.
Working on regular-sized Bo-Jest


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