1968 Larson All American

[coolbri70]

Re: 1968 Larson All American

it is at its lowest setting now i am new to this so i just put it on like the po had it, and it did fine aside from revving up now and then, i thought it must be too high up so i trimmed it down a hole which seemed to stop the revving but now it plows the water, i mean this thing rides flat on the water no bow up at all hit a big wake and had water splash over the bow, could the prop be slipping due to mr larsons million bubbles theres alot of bubbles coming out the back, would a prop slip in all those bubbles, and theres spray like 20 feet to either side of the bow, big spray, i mean i see spray from other boats, mine is times 10, in post 92 you can see it to my side and its trail in the other pic

 

[Willyclay]

Re: 1968 Larson All American

would a prop slip in all those bubbles, and theres spray like 20 feet to either side of the bow, big spray, i mean i see spray from other boats, mine is times 10, in post 92 you can see it to my side and its trail in the other pic

I am in total agreement with you that what you describe does not seem right. If what you are calling "prop slip" is the prop loosing bite in the water and the motor revs higher, then it could be caused by all those bubbles. I'll let the experts decide whether that is properly called ventilation or cavitation. When your wife, excuse me "Admiral", has been driving at planing speed or higher, have you looked over the transom and observed the anti-ventilation plate? It should be just on top of the water. Too low and it creates extra drag and spray in the wake. Too high and it will suck air into the prop. As you have already learned, trim affects this situation.

To achieve the highest speed for a particular boat, the boat's "wet area" has to be at a minimum compared to other speeds. I would expert your boat to be like most others and normally run with a slight bow-up attitude for best results. Since load distribution is critical on a small boat, do you have anything stored/loaded up in the bow area?

Finally, on one of my previous boats with a non-PT&T motor, it could not get it trimmed just right with the pin settings the motor bracket provided. I started experimenting with sleeves of different thicknesses over the pin until one seemed to work better. FYI, I tried hard copper pipe, PVC and water hose. PVC was my final choice. I guess it made a slight difference in the trim and my boat found its "happy place".

You might want to start a new thread in the Prop Forum about this particular problem and see what the prop experts have to say. There are some very experienced and sharp members over there who can probably solve this mystery. Sorry I am not more helpful.

EDIT: Check out the link below. Disregard the dimensions but note the diagram of how motors should be mounted, i.e. the bottom of the hull parallel with the bottom of the cavitation plate. Maybe your hull just will not work with this approach. Good luck!

http://www.boatmotors.com/ref/shaft_length.html

 

[coolbri70]

Re: 1968 Larson All American

thanks i will look into that as i'm thinking this motors "happy place" is somewhere between those holes

 

[johnny howe]

Re: 1968 Larson All American

i own a 66 all american, my boat seems to spray alot towards the side and out the back straight up to the sides, i think my boat is a little waterlogged on the right side , i have to lean abit towards the middle to straighten out the ride. i think my cavatation plate is riding to far under water, blowing water straight out the sides of the prop. i think compared to other boats i see also, the larson seems to spray out alot, can you almost touch the water spraying off the front bow? when i takeoff the bow rises then settles down on plane within 15 seconds or so.

 

[Willyclay]

Re: 1968 Larson All American

i own a 66 all american, my boat seems to spray alot towards the side and out the back straight up to the sides,

Johnny, thanks for posting your experience with an All American and it sure does sound the same. However, before we go crazy here and declare it to be a bad design, we need to make a closer comparison because I believe the AA hull design changed significantly during the 1960's. For instance, I think the early models had soft chines (round) and Brian's has hard chines. The bottom strakes may be part of the "Million Bubble Ride" thing but I don't know how much of that was marketing hype and how much was a real design feature. If you have pictures of your hull especially looking forward at the transom posted in another thread, please provide a link or post them here. It might help everybody get their arms around this situation. Also, we cannot rule out the motor mounting height issue for either one of you until some testing is done!

 

[coolbri70]

Re: 1968 Larson All American

i raised the motor on the transom 1 inch, the cavitation plate is more even with the keel, trying it out today hope for improvment, should be less drag now

 

[Willyclay]

Re: 1968 Larson All American

Standing by for the results. I saw your thread about the linkage problem. Good luck today!

 

[coolbri70]

Re: 1968 Larson All American

the linkage to the timing advance kept falling out, need to replace the ball socket piece, when it was working the water was up to the bottom of the flange above the cavitation plate, still need to go up with it i think it does have better posture in the water than before

 

[Willyclay]

Re: 1968 Larson All American

Sounds positive! Too bad about the linkage.

 

[coolbri70]

Re: 1968 Larson All American

so i'm waiting for it to cool off wow what a scorcher, i,m going to raise it this evening, maybe all the way to the top as the water is flowing at the bolt heads for the lower unit should the exhaust holes be out of the water as well?

 

[Willyclay]

Re: 1968 Larson All American

View attachment 155466 should the exhaust holes be out of the water as well?

If you are referring to the six holes above the AVP in this picture, I do not believe they are exhaust holes. I think they are water inlet holes for neutral and reverse gear operations. All your exhaust exits via the prop except at idle when water pressure creates enough back pressure in the lower unit to force exhaust gasses out the exhaust relief holes high on the exhaust housing just below the lower cowling.

 

[coolbri70]

Re: 1968 Larson All American

before i raised the motor at all the water was just below the stripe at wot, i raised it 1 hole and the water was just at the bolts i was going to raise it again the avp plate @ water level @ wot ? would make the 6 holes out of the water

 

[coolbri70]

Re: 1968 Larson All American

i was going to do fri night but a bad storm came and took our power :facepalm: so instead i spent the weekend running chainsaw, cleaning, and camping at the house it was hot so i was in the pool alot then tried to go boating and it was too crowded so i turned around and went home just got power back today

 

[coolbri70]

Re: 1968 Larson All American

some pics of the boat in the driveway not finished yet but having fun with it

 

[TruckDrivingFool]

Re: 1968 Larson All American

Looking good Bri, I thought of you today as I was looking in my manual and decided to scan this for ya

#8 Water Outlet

I'm not sure if you're asking if they should be out at rest or on plain. But I would think shouldn't be a problem if they're out so long as the LU is deep enough to still pump.

 

[coolbri70]

Re: 1968 Larson All American

thanks TDF i think i need to raise it more water is catching on the round edge of the upper shaft at wot:facepalm: i think only the sharp edge of the lower unit should be in the water for less drag i read the avp should be near the top of the water at wot

 

[coolbri70]

Re: 1968 Larson All American

after the storm the downed trees and 3 days without electricity, then a visit from the inlaws who got here friday, they left at 12 today, i cleaned the gutters and then found the time to raise the motor i went all the way up with it, hope this gets the avp closer to the surface

 

[Willyclay]

Re: 1968 Larson All American

View attachment 157101 i went all the way up with it, hope this gets the avp closer to the surface

Looks good to me!

 

[coolbri70]

Re: 1968 Larson All American

so i had a chance to try it today, think it needs moved back down a notch had trouble with getting grip with the prop a few times:facepalm: it would blow water like a fire hydrant

 

[Willyclay]

Re: 1968 Larson All American

Unfortunatly, this is the only accurate method for finding that elusive "sweet spot". Hang in there, you can whip it!