1975 SeaCraft CC , 18' ..Transom height change ??

[striker]

Hi there all , first post here . Nephew has recently aquired an 18' CC and we are taking it apart ... of course he is doing most of the get started (dirty grunt) work , I got my own Montouk B.W. going on right now (or I should say waiting for me to start up on it again , I'm lazy , it's my 8th boat) .

His boat - Gunnel and deck cap is off , T-top is off , rub rails off , interior shell is out (has locker each side of trans.) , tank is out . He is working on seperating the existing ply from the glass transom (in progress , no problems yet) .

I want to raise the transom height 5" when we do the rebuild . It is 20" from top to bottom as it is now . (for clarity because I may not always use correct terms to identify things , I'll elaborate like this , "that is from where the motor bracket would seat down full tight - to the very bottom of the V (keel) in the center") . Again that measurement is 20" .

When rebuilt I would like it to be 25" if that will work ?? I haven't any problem with the rebuild part of it (yet) , but would like to know we have some friends here for future as this project goes along .

So my question is ... if I rebuild from existing 20" , to desired 25" , what shaft length should the "New" motor be ( he thinks he will get a 150 hp) ?? Would a 25" transom require a 30" shaft motor , and if so , will that work OK on his boat ??

Is there anything unusual about a 30" shaft motor that we should think about (compared to other outboards) ??

Can he purchase (New) a 30" shaft motor just as easily as a 25" shaft ??

Ah , I think I'm picking up 2 sheets of 3/4" Okume on Mon. to get ready . I'll be giving him a list of epoxy and fabric supplys to get soon .

thanks in advance ... will be checking back soon , Dan

ps., ... it's not that I can't go talk with the marina guys , it's more like I'd rather start here ... it's his boat , I'm just the ol Uncle , lol .

pss., ... no , do not want a seadrive bracket

[GroveGuy]

Hey Striker,

Several of us during rebuilds have raised the original transom from 20" to 25" and from my personal experience I highly recommend doing it.

A 25" transom would ordinarily hold a 25" shaft engine. The exception might be if you wanted to use a raised jackplate mounted on the 25" transom which might allow a 30" shaft. I would not imagine the need for this setup though, especially for an 18 footer.

There are plenty of folks around here who are much more knowlegeable than myself and can provide great advice along the way. Posting some pics of your progess will help tremendously!

There have also been numerous step by step threads posted on this subject over the years and I highly recommend a liberal use of the search function to see how other Seacraft owners have rebuilt their transoms.

Best of luck and welcome to the site

[striker]

thanks Groveguy ... so if I am understanding correctly , a 25" transom " does not " require a 30" shaft motor to keep the gear pod and prop at the correct depth in the water .

In other words , a 25" transom height requires a 25" shaft motor as standard proceedure ??

Nephew is thinking because he has a 20" transom as it exist now , that a 25" shaft motor would be "required" to get the pod and prop below the keel and in the correct position .

I am just trying to be sure about this before I raise his transom height 5" more . I should know the answer to my own question by now , but the Nephew has given me reason to doubt my understanding .

[dlb511]

A 25" transom is what you want. Most contemporary outboards are equipped with 25" shafts. 25" measured from the top of the transom to the bottom of the keel. On the motor it is measured from the bottom of the bracket where it mounts on the transom to the cavitation plate on the lower unit. 25" is the "new" standard. 5" more freeboard and a real safety factor. Don't even consider doing all of that work and leaving it at 20".

[McGillicuddy]

Welcome aboard, striker.
That is correct, a 25" transom requires a motor with a 25" shaft. A 30" shaft would run way too deep creating drag and very inefficient propulsion. In fact it is quite likely that you would never attain optimum rpms putting your motor at risk. When you get around to mounting the motor you'll want to set it at height where the anti-cavitation plate is about 1 to 1-1/2" above the keel at level trim (anti-cav. plate parallel to keel).

If you currently have a good 20" shaft motor and not certain about buying a new one, there is likely a 5" shaft extension kit available for that motor for $500-600 from Bay Mfg.

Good luck with the project.

[Bushwacker]

30" motors are now available, although not as common as 25" versions, so probably quite a bit more expensive, and probably only available on the larger motors. Probably not needed for an 18 as long as you stay with a fairly light 300-350 lb 2-stroke motor. The transom cutout would be 30" above the keel if you decided to go that route. Although Skip & Carla are planning to mount twin 25" motors on their ex-raceboat 21, Skip also set the transom cutout up for a single 30" motor in case someone in future wanted to convert it to a big single, but that's a MUCH bigger boat than an 18!

[striker]

Thank you all so much for clearing up any doubt and confussion I had with the transom and shaft question .

I have it clear as can be now , 25" transom = 25" shaft motor . Nephew has been studying this site also for awhile , he told me about it . It's been very helpful so far being able to see in advance what he's getting into from everyones post and others pics.

My guess is he will chime in sometime in the future ... he's got lots of pics. so far and they look almost exactly like everyone elses that got opened up . pretty cool I think !!

thanks again gang , Dan

ps., ... I believe he told me the 150 hp he's considering weighs in at 374 lb. ... Optimax

over and out , for awhile