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Danny
09-04-2001, 09:28 AM
Drove a 1970 21GT this weekend, it had a 454 and Trs drive put in it in the mid 80s.
The engine turned only 4200 rpm. Should be closer to 4500?? The strange part is that there was very little if no neg trim. With the trim tucked under as far as it would go the boat was slow out of the hole and very light in the front end and would immediately porpoise if you put any trim on it at all. Put the tabs all the way down got on plane more quickly the second time but still not as fast as I would have thought. Tabs definetly kept the bow down but as soon as you take the tabs off the bow lifts and you have to run with the trim all the way in or down.
Going to try a lesser pitch prop to get the rpm up a bit and maybe some cup to give more lift to the stern and get the bow down.
Anyone else have the same set up, what are you using for prop?
The Merc is definetly heavier than the original Volvo and I don't think that should be a factor on it's own but still could contribute to the overall problem. I assume weight in the front would help to counter-balance and keep the front down but this is not really solving the problem.
When they changed from thr Volvo to the Merc trs if they got the X dimension wrong, ie drive to high, would this change the trim capabilities? If the cavitation plate is too high in relationship to the hull then the plate would actually be above thwe water behind the transom. Anyone now the the proper mounting height for the trs?
Would a stern jack (drive extension) help to eliminate ther problem?
If this boat is set up properly should you not have a fair amount of trim range and only have to use the tabs for better hole shots and levelling the ride?
Any thoughts, input or ideas would be greatly appreciated, my friend is getting frustrated.
Thanks for the help
Danny

Forrest
09-04-2001, 11:21 AM
How is the compression on that 454?

Danny
09-04-2001, 12:26 PM
Forrest
To the best of my knowlegde the compression is good. The owner had it tested last fall when he bought it,I don't remember the figures but I know they were acceptable and doesn't have many hours since then. You thinking low compression results in low rpm and lack of power? The boat does move well when you get it going, high 50s with 5 people and full of gas, but again stilllight in the front with abilty to trim the nose down, only comes down with the tabs.
Your Hornet had the same power package, did you have enough range in the trim?
Too bad you sold it(too bad for me). If I had sold my 16 I was going to drive south and take a good look at your Hornet. Do the Hornet and GT rides compare? I've been eyeing up another GT with the orgianal 350GM/ Volvo 270 combination.
Thanks
Danny

BigGrizzly
09-04-2001, 02:10 PM
I have that package in my 22 Criterion. cavitation plate should be 3/4 inch above the bottom of the boat and level with it.
I seriously question the speedometer. that means you would turn a 35 pitch to do that speed. If it is a 330 it should turn about 4500->4700. If it is a 420 then 4800->5000 is where you want to be.

Randy

Forrest
09-04-2001, 02:59 PM
Hay Randy, I think he was saying the the Hornet was retrofitted in the mid 1980s with the TRS setup rather than it runs in the the mid "80s". By all accounts, it sounds as though you could be down on power for some reason. Try to prop it to top out in the range where Randy shows above. The big block should pick the boat up fairly well, and run good on the top end when propped for the correct RPM range - even if it is stock. Assuming that you are runnning 1.50:1 gears in the TRS, I would start with 21" pitch prop and then go from there.

jwright
09-04-2001, 04:22 PM
Well I have a 1976 21GT with a 280 TRS driveline (350 Chevy, merc trans, TRS drive).
I spin a 21" prop at 4500 rpm and hit about 54 mph on GPS.
The hull is unique in that it has substantial rocker in it, not hook. If you sight up the chine from the transom you can see that it is not straight, the chines rock upward. This creates alot of "natural" bow lift. (perfect for an Arneson I bet!!!) The fuel tank is also fairly far aft and is BIG at 60 gallons. From my experience these things add up to a boat that does not require a lot of trim to get free of the water. for the best ride in mine on flat water, I trim the drive up and then take my tabs down just a little and it runs great. That eliminates the propoising I would get if I only trimmed the drive up with no tabs.
I think the hull is not the best for flat water speed, but is awesom in chop! It always lands on the aft part of the hull, just flys across and keeps the bow up. I also diosappointed with my hole shot too.
I would like to talk to you more about it if you want. I LOVE this hull so much despite its flaws. When I get in rough water it is the greatest boat for only being 21'.

BigGrizzly
09-04-2001, 08:25 PM
Now I see Forrest. According to my old manuals the TRS had two ratios the 1:50, and the 2:? ratio in both left and right drive. the rotation is in the lower unit. In any case with the small 330 in my Criterion I turned a mirage 23 in that range.

Randy

Danny
09-06-2001, 02:26 PM
Thanks for the input gentlemen.
I think the first thing we are going to do is play with props to try and get the rpm up a bit. We will also clarify the drive height and see if it comparable to Randy's setup.
Question Does a cupped prop provide more lift to the stern of the boat and therefore keeping the bow down?
Danny
If anyone sees a GT project boat let me know I'm willing to travel to pick one up, fairly limited supply up here

Rick
09-06-2001, 03:11 PM
I have a good original 70' GT-21 that would make a great project boat. Good Mechanicals. Twin 351's.

EricG
09-06-2001, 03:23 PM
Rick
Welcome to the board.

I'm assuming your GT is this one?
http://home.talkcity.com/RallyRd/egudgel/gttwin.html

If so, do a search, it's been the subject of some previous discussions here on the board (not to mention, a minor obsession of mine ever since I saw it) ;)

What else can you tell us about it?

EG

Rick
09-06-2001, 03:43 PM
Yea, That's the one. I've owned her since 1989. The boat has been painted in a previous life. Motors are the original Holmon & Moody as are the outdrives, however I had the motors rebuilt 6 years ago. Interior except carpet, and gauges are original as far as I know. She has been in storage for the past five years. Had her in the water last weekend. She needs a little sorting, but generally seems OK. Also have the original trailor

RickSE
09-06-2001, 04:12 PM
Wow, so the Twin 21-GT is back. I along with others have been wondering what happened to that boat. It's been a while since we've heard anything about it. That's one cool boat. Sounds like it's for sale. What's the asking price?

Rick
09-06-2001, 04:24 PM
I want what I have in the motors which is 10K.

BigGrizzly
09-06-2001, 07:28 PM
Please take me for a ride. Saw the the twin Gt 21 when it first came out and though it way cool.

Randy

Rick
09-07-2001, 08:18 AM
Well if your in the Southwest Missouri area I would be happy to give you a ride. You can reach me at sales@superiorgearbox.com . It seems that this boat is such a rare example that no one really knows what it's value is. Do you have any ideas? Production numbers?

Danny
09-07-2001, 08:53 AM
Rick
Interesting boat, I wasn't looking for one with twins, the boat is so unique you certainly wouldn't want to repower it with a single. You certainly have an arguement here for maintaining the originality of the setup in a classic boat like this. Toying with the idea of selling my 16, if I move in that direction I may plan a road trip to take a look I'll put your email address in my book.
Thanks Danny

Rob
09-08-2001, 11:58 AM
Rick:

I'm friends with a previous owner of this boat. Who did you purchase it from?

Rick
09-09-2001, 04:40 PM
Rob, I think you must have known the previous owner. I hadn't met the person only the broker at Port Arrowhead. I was told he was an oral surgeon out of K.C.. Would they allow a boat of this size on Lotawana. What do you know of this boat. I had it on the Ozarks first then Tablerock and now on Stockton Lake.

Rob
09-09-2001, 10:59 PM
That sounds like the right person. I know he was a doctor of some sort. They kept it at Lake of the Ozarks. Do you happen to remember the name?

olredalert
09-10-2001, 09:29 AM
Rick,

I knew the original owner(although I cant remember his name).Rode in your boat when it was,maybe,2-3 months old.Ran good but serviceability was difficult as I recall.Owner traded it back directly to DONZI as he was a good friend of John Chisholms(owner of DONZI and great guy).Wonder if John could be persuaded to pop into Sarasota for a bit?The new 21GT was powered by biggest 427 Mercruiser that could be bought with NO.3 Speedmaster unit behind.Rode in that as well and it possotively flew.Was the brightest yellow I ever saw with livid bright red interior.
Does your twin have a trailer with it?Is the trailer serviceable?What sorting does the boat need?How were the engines built?How far over are they(30,60,etc.)You can E-mail me direct if you would like....redalert@massnet1.net.Am interested!!!!......just.......ol red!