View Full Version : GT 21 measurements

01-27-2012, 03:25 AM
Finally getting to the GT, scary......but fun. Deck is loose and ready to lift off to redo the stringers but she was a twin and I'm putting in a single. I put a couple of old crank style camper jacks on blocks to lift the deck high enough to pull the trailer out, but I ran out of courage before I ran out of blocks. LOL. Guess I need a crane or something.

Anyway, can someone tell me a couple of measurements for a single engine GT, I need distance between the stringers and the stringer height?


Scott Pearson
01-27-2012, 07:48 AM
Stringers should be 30" apart from the inside. Not sure of the height. I would keep the boat a twin setup. Very rare and only a few made.

01-27-2012, 08:23 AM
Somewhere on another thread here I think I remember that just 2 of these GT 21 twins are known to exist.....nevertheless, it's value does not seem to reflect that rarity.

It's your boat, so you should make it the way you want it. I would document the refit and when someone is willing to pay six figires for a twin, you can hire a professional to switch it back if you care to. In the mean time enjoy it.

(P.S. I'm NOT the owner of the other GT 21 twin)

01-27-2012, 09:37 AM
do you have a hull number?pics would be awesome.

[ QUOTE=woobs]Somewhere on another thread here I think I remember that just 2 of these GT 21 twins are known to exist.....nevertheless, it's value does not seem to reflect that rarity.

It's your boat, so you should make it the way you want it. I would document the refit and when someone is willing to pay six figires for a twin, you can hire a professional to switch it back if you care to. In the mean time enjoy it.

(P.S. I'm NOT the owner of the other GT 21 twin){$pagetext}[/QUOTE]

There a very few remaining twin setup GTs, the GT in itself is a fairly uncommon boat and when in very good original shape or very nice restored shape do fetch more than a more common classic.
an Example would be the blue and white twin 351 setup which sold some 7+ years ago here. That boat sold in the 17-19k range. The nice blue and white single merc lake george GT which also sold in the mid teens a few years back. That value was higher than other classics selling at the time. There were 2 other GT twins that popped up recently within a few years a yellow twin volvo 170 and a tan twin volvo repowered with merc fords. The value of those of course were lower as they came up in the poor economy.

Just for the record 7 twin gt's left the factory

2 volvo 170 volvo outdrive
1 HM 235 hp302 volvo outdrive
3 HM 290hp 351w volvo outdrive
1 HM 400hp 427 V-drive

you have a rare subset in a fairly uncommonly seen classic. I would keep it as it was but that is me.
I think the dash console on a twin GT is very cool sort of like the control panel on an airplane with all the gauges. Again yes it is your boat and build as you see fit, but realize that the value on a boat like that is in uniqueness and originality. If that twin 427 boat ever surfaced you would see a feeding frenzy , and the dark underside of a board behavior just like when a rare criterion or other boat surfaces.

good luck on the project

Greg Guimond
01-27-2012, 09:51 AM
Would love to see some pictures of the rare beast and I cast a vote for keeping the twins :yes:

01-27-2012, 11:13 AM
here's a few pics I'll see if I have any of the yellow one

01-27-2012, 11:32 AM
yellow one

01-27-2012, 11:35 AM
Yes, I agree it is nice to keep the rare ones original, but to what end?

The cost of refurbishing another engine and drive (for the twin) alone is more than the difference in resale. Then there is extra running and maintainance costs over the life of the boat. So, on a dollar for dollar rationale it doesn't pan out (not even close).

I have seen many classic boats, some valued in the 100's of thousands of dollars that have had extensive refits including non original power. It has not greatly detracted from their value and has actually made them more enjoyable to use (the original purpose). As long as it is documented it's all good. 40 years from now if the boat is actually worth it, someone can refigure it to original specs.

The issue of "the last few standing" is romantic/emotional or historic, or maybe has somthing to do with brand loyalty but, other than bragging rights to a rare model, it does nothing. We can all say "it's a nice boat" though.

On the practical side, you must consider the utility derrived from this boat. The owner bought it for a reason. I'm sure the refit of this boat helps the desired application of its use. To maintain a configuration which is not conducive to it's use does not make sense. Makes less sense if maintaining that configuration actually detracts from the intended use or increases costs for the intended use.

Now before you think I'm a totally heinous person without respect for provinance, (I've been through alot of this with the Porsche Club of America..). I would not for example, repower an original 1973 911RS 2.7 Carrera with a 3.2 L motor...but it's inherant value reflects this.
Similarly, If this GT 21 twin is such a rare and valuable boat then theoretically someone should step up and offer a very large sum of cash to buy it (and keep it original). As it's only worth what someone will pay, I fear keeping it original, while nice a sentiment just isn't practical.

Bottom line is...it's up to the owner. He should make it how he wants it and enjoy...no matter which configuration he chooses. That way he can't lose.

01-27-2012, 11:56 AM
If you want, I have a GT21 sans engine right now and can get you pics and measurements this weekend. I'll pm you my cell #

Morgan's Cloud
01-27-2012, 01:44 PM
Per Matty ''1 HM 400hp 427 V-drive''

That must have been a beast .... Would I ever love to have seen a photo shoot of that thing the day it rolled out the door !

01-27-2012, 03:51 PM
[ QUOTE=$originalposter]Morgan's Cloud
Per Matty ''1 HM 400hp 427 V-drive''

That must have been a beast .... Would I ever love to have seen a photo shoot of that thing the day it rolled out the door !

{$pagetext}[/QUOTE]hell yeah me too!!!!!!!!!!!!

Sweet Cheekz
01-27-2012, 04:32 PM
You make some valid points but the only thing I say is that there are plenty of wrecks and junkers around of the single engine gt's so why not buy one of those, save all that engineering and move the twin for what he has into it. The rare boats may not be fetching top dollar today but when there are only 7 I doubt its going down anymore. If redoing and selling is the goal its a losing proposition regardless of the make for a very long time if not ever. Just my .02 worth


Scott Pearson
01-27-2012, 06:03 PM
Rob, I would be very interested in your 21 GT. Maybe we can make a deal and you can find a single engine 21 to restore. I agree with Matty and Parnell.

01-27-2012, 07:09 PM
woobs, there is a board member here that has a phenominal turn-key 21 GT, on an aluminum trailer, ready to go today, for about 1/2 to 1/3 what it would cost to restore yours, then you can sell your's to someone else, and save about 30k... thats a fact

for the record, contact me by PM, and i'll put you on to him, he lives about 10 minutes from me, also I have no interest in buying yours, nor will I get underneath a deal, just trying to help you get on the water

01-27-2012, 08:25 PM
Hi Buiz,
It's not my GT 21 twin...I was just being the Devil's advocate....(I was in a bit of a "mood" this morning).

Boat belongs to Rob (Vertigo). And if this works out it's a great solution...to a problem we never had!

The poor guy just asked for some measurements...and now we have found buyers for HIS boat as well as found him a new turnkey boat to replace it with.

I'm still chucklin' here.....:nilly:

01-28-2012, 09:00 AM
vertigo it is your boat build it as you see fit. i stated what i did not cause i was in a mood but as fact.

historically rarer boats do fetch more money and do so because the buyer wants that model. it has been seen here over and over even in a poor economy x18 and corsican fetch more cash than a 18c apples to apples in the same shape and vintage.same for an f22 or criterion over a 22c again apples to apples.

i am not sure what your expectations are for the boat, looking for speed or general cruising in bigger water. practical very rarely is used in a sentence with a donzi classic. they really aren't pratical boats low freeboard no storage but i don't think that is what hook all of us.

vertigo i think you have the yellow boat i posted pics of to me that would be the perfect pratical donzi higher freeboard and with the safety twins afford would be able to explore a larger boating world.
yes twins are more expensive but a 6cyl volvo/ volvo drive is one of the most bullet proof packages. the cost to re work the dash and transom to single needs to be figured in too. the transom is different on a twin then a single you'll need to figure out what power than make sure the transom will work. i am not saying it won't but if it were me i would check to make sure it would.

good luck on the project

joseph m. hahnl
01-28-2012, 09:09 AM
Your going to change what to single?:wink:


It's not nice to fool with Donzi nature:biggrin:

01-28-2012, 11:11 AM

if you have a hull number or serial numbers on the drives or motors i can help id the boat and get some history on it
for you

01-30-2012, 04:08 AM
Thanks for all the advice, I honestly do appreciate it. Yes it's the yellow one, and I've struggled with this for a couple of years now as to which way to go. The 170's are reportedly rebuilt, and a mechanical witch doctor buddy got them both running....after a few vertical flame throwers, but my concern is once it's all together it may turn out to be more of a museum piece than a usable boat. I know a single would handle well, but with twins it's kind of a wild card. May be great, may be a dog. Problem is once I rebuild the stringers for twins I can't just throw in a single if it doesn't work. I also picked up a spare 170 that strangely enough came with a closed cooling system (first one I've ever seen, which doesn't mean much).

However I also have a rebuilt 454 sitting in a friends shop that would go nice in front of a bravo 1, with a predictable result, (usable boat). I did put it up for sale for a while to see if anyone wanted to preserve the heritage, but no takers. Boats don't seem to have the same collectability as cars so rarity seems less valuable that practicality or usefullness??

Deck has been painted previously, but hull is still in gel. Looks to me like the stringers were replaced once, or at least covered over with cloth, but they are gone from the transom to about half way up the fuel tank. The bolts for the transom shields were sinking into the transom and it showed a little delaminating so I'm pulling the deck to hack and slash. Last week it was to rebuild stock with the mixed sound of 12 cylinders and 6 carbs, but my fellow boaters here say it will be a garage queen.

First day off tomorrow so I'm headed to the paint shop to work on the deck and I'll get the numbers and some pictures. I'd love to know its history, thanks for the offer!!

Rob from the wet coast.

01-30-2012, 04:37 AM
Title lists the boat as a 1974


I remember looking at the sticker on the side of the gauge pod. Both engine serial numbers are also on it, and they match the engines which I though was kinda cool.


01-30-2012, 07:39 AM
hull 69 started 11/72 completed 12/72 sold to dealer tiffany

the last of the mohicans, the last factory built gt21 twin

01-30-2012, 07:57 AM
those Volvo 170's are more reliable than the sun coming up.... get the carbs synched right, and don't look back

if you ever need a manifold though, they are getting pricy, there are 2 on ebay now for about $1200 EACH

what about repowering it with a pair of V6 Vortec Chevy's? 205-220hp 4 bbls? that thing would fly, and you can buy parts at any 7-11...

01-31-2012, 12:33 PM
Thanks for the info.

Any leads on the other gt21 170's twin? If I had an idea of how this boat would handle with the twins it may sway me back in that direction. This is alot of work so I only want to do it once....


Sweet Cheekz
01-31-2012, 05:53 PM
Good idea to get all the info you can and here and on org you will find it. Good luck either way


02-05-2012, 03:27 PM
Here goes, sorry about stringer pics, she's covered for the winter and I was working through transom cutout. Time to hit the gym...






Stringers 32 1/4 inside at front lower mount holes

30 3/4 transom to c/l of front lower hole

Overall stringer height 7 1/2

3 1/2 to c/l bottom mount holes

Bracket Upper Transom Holes (B) 2 1/16 on c/l
Height of inverted "triangle" 2 3/4 on c/l

10 1/2 c/l from (A) to (A)
4 c/l from (C) to (C)
5 3/8 from c/l of (C) to face of stringer
Platform upper height is 5/8 below c/l of (A)
Brackets aren't exactly "square"
Volvo 280 outdrive SBC
Good luck!