Dumb I/O questions, Seahawk 215

[btravlin2]

Sometimes the most simple questions are surprisingly hard to find answers to. I've never owned an I/O, and I'm looking at a 1984 Chris Craft Scorpion/Seahawk 215 WA with a 5.7. The draft is borderline for the shallow inshore waters around here. I'm trying to determine if I can run this at higher tides while heading to the inlet to get offshore. That means having 28" underneath for part of the way over a soft mud bottom.

Judging by the waterline, the hull itself draws 16". Since the lower unit is off right now I can't tell what the total standing draft is. It's an Alpha 1 drive.

I could use help with these 4 questions:

-what do you guess is the standing draft with the complete outdrive down?
-what might be the planing draft?
-how high can the lower unit be trimmed up at slow troll speed while still making way and keeping water in the water pump? And so what would that mean for total draft while trimmed up?
-does an I/O outdrive kick up like an OB when running aground?

BTW: I've tapped the engine mounts, stringers, transom, and hull. Can't find any dull thuds. Both the motor and outdrive are freshly rebuilt, and I see no stress fractures. The fuel tank has recently been acid cleaned and pressure tested for 24 hours. I think it could be a good boat for within 40 miles here in the Gulf.

Thanks in advance......

 

[Fishermark]

Re: Dumb I/O questions, Seahawk 215

I don't know the specific answer to your questions, but we too have extremely shallow water here where I boat. 28 inches is a luxury at times here in SW Florida. I have found it reasonably easy to trim up sufficiently to get through any shallow water that we encounter. If you like the boat and it is just a case of having to get through some skinny water on occasion, I say go for it!

 

[Jonnybbad]

Re: Dumb I/O questions, Seahawk 215

Sounds like your prop and skeg are gonna get polished up nice, but you should make it though 28" of water fine if there aren't any high spots. I sure wouldn't think about traveling at planing speed though such shallow water though. I'm sure you would experience binding in the u-joints well before you would expose the water intake area of the lower unit. Not to metion the prop would be sticking out of the water before that also. I don't even think the water intake is above the waterline even with the drive in full up trailer position on either of my alpha one boats, which you would not want to run the motor in this position anyways. There is some degree of protection in the hydraulic system if you hit your drive on something going forward only, but I wouldn't count on in saving you in every situation (I would suggest you travel slowly in shallow water). I'll try to take some measurements for you tomorrow.

 

[tpenfield]

Re: Dumb I/O questions, Seahawk 215

I could use help with these 4 questions:

-what do you guess is the standing draft with the complete outdrive down?
-what might be the planing draft?
-how high can the lower unit be trimmed up at slow troll speed while still making way and keeping water in the water pump? And so what would that mean for total draft while trimmed up?
-does an I/O outdrive kick up like an OB when running aground?

Thanks in advance......

Add 12" to the hull draft for the outdrive down.

Maybe 6" less than standing draft

lower unit can go up all the way and run at idle, although not recommended, but do-able. You will still have about 2-3" extra draft with the outdrive up.

The outdrive will try to kick up, but expect some damage to lower unit and prop.

 

[btravlin2]

Re: Dumb I/O questions, Seahawk 215

I don't know the specific answer to your questions, but we too have extremely shallow water here where I boat. 28 inches is a luxury at times here in SW Florida. I have found it reasonably easy to trim up sufficiently to get through any shallow water that we encounter. If you like the boat and it is just a case of having to get through some skinny water on occasion, I say go for it!

Fishermark......are you using an I/O? How far up can a Mercruiser Alpha I be trimmed at slow troll speed without binding or causing harm to the u-joints? If my total draft with OD down is 28", I'm wanting to know if I can trim up to give me 24" draft with both prop and intake sufficiently submerged, and not stressing the u-joints.

This would be for a stretch of about 300 yards. After that I'm in deeper water.

 

[Another retired guy]

Re: Dumb I/O questions, Seahawk 215

How far up can a Mercruiser Alpha I be trimmed at slow troll speed without binding or causing harm to the u-joints? If my total draft with OD down is 28", I'm wanting to know if I can trim up to give me 24" draft with both prop and intake sufficiently submerged, and not stressing the u-joints.

This would be for a stretch of about 300 yards. After that I'm in deeper water.[/QUOTE]


I'm in a similar situation to you. I have to travel about 200 yards along a very shallow channel to get to deeper water. I run my alpha 1 in full trim up position at idle speed. Even have to go a little bit into trailer position to get over a sunken log Been doing it for a year now with no problems - uj's will take it as long as you keep it slow!

 

[Fishermark]

Re: Dumb I/O questions, Seahawk 215

Fishermark......are you using an I/O? How far up can a Mercruiser Alpha I be trimmed at slow troll speed without binding or causing harm to the u-joints? If my total draft with OD down is 28", I'm wanting to know if I can trim up to give me 24" draft with both prop and intake sufficiently submerged, and not stressing the u-joints.

This would be for a stretch of about 300 yards. After that I'm in deeper water.

Yes - I have an I/O. As mentioned above you can trim all the way up at idle - even up to the trailer position. (Not that I would recommend that and not that you will need to go up that far.)

The real concern when trimmed up too high is the lack of "side to side" protection for the outdrive. Notice the outdrive will go up beyond the tabs that help give it side to side stability. So far as binding the u-joints, remember they are designed to allow movement. The thing most people forget is that whenever you turn to the left or right you are causing the u-joints to turn and move as well. Far more than simply trimming up.

But yes, keep it slow and you should be fine.