Drying out an old boat.

D

delan

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Joined
Oct 10, 2004
RO Number
15501
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I have a 70's Mako 236, that's the inboard 350 chevy model.
Center console.
The boat doesn't perform as well as it should, The motor is fine, the shaft has been trued, the strut is inline, I've propped it to reach 4600rpm lightly laden.
The bottom is fresh.
I'm getting 27kts at 4600. I've talked to several other 236 owners and they're getting about 10kts more at similar rpm's.
I suspect the foam that was used has absorbed water, and the boat is carrying more weight that it should. I was thinking about putting a dehumidifier in the bilge and letting it run for a week or so, do you foresee any problem with this?
Regards, Joe Miami Beach.
 
Have the boat weighed on a boat sling and compare it to the original specifications. If it's in the core I doubt a dehumidifire will help at all.
 
If wt. was the problem, wouldn't you be getting less rpms at WOT?
 
quote:
Originally posted by Billylll

Have the boat weighed on a boat sling and compare it to the original specifications. If it's in the core I doubt a dehumidifire will help at all.

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The boats were foamed for flotation, that's where I think the additional water is.
 
quote:
Originally posted by Gregory Saracco

If wt. was the problem, wouldn't you be getting less rpms at WOT?

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I've only owned the boat for six months, but I went through 3 prop adjustments to be able to turn the rated rpm's.
It's neither over or under propped.
 
Do you have a cup in your prop? I had simiular issues with a former boat (1976 vintage Sea Ray). Couldn't get my RPMs up high enough, and everybody kept suggeting reducing pitch, reduce pitch some more, reduce pitch some more... I got got the rpms up to specs and speed had dropped to a rediculous level. I was just spinning the wheel and going nowhere. I argued with the prop shop and had them put a cup in the prop, and the boat gained significant speed with minimal loss of WOT rpm. I gained 7 knots, and only lost 200rpm

If you were successful in drying the foam and reducing the weight your RPMs are going to increase and you will need to adjust the prop again. However, I doubt that any drying weight reduction will last. Water will find it's way back into the foam unless you are able to replace the foam.

There is also a difference in a clean bottom and a newly painted bottom. New paint always goes faster. I'm always amazed at how much faster the boat goes with new bottom paint.
 
Hi Paul, yep I have a medium cup in the prop, probably 20 degrees. and the bottom paint is new.
I'm going to try the dehumidifier, the boats 30 years old, I posted the question to see if anyone had a reason not to do it, that I hadn't contemplated.
I'll let you know how I get on.
 
quote:
Originally posted by delan

quote:
Originally posted by Billylll

Have the boat weighed on a boat sling and compare it to the original specifications. If it's in the core I doubt a dehumidifire will help at all.

Click to expand...


The boats were foamed for flotation, that's where I think the additional water is.

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Agree. I had a Formula F233 and bet I pulled 300 pounds of water filled foam from beneath the deck.
 
The chance of getting out significant amount of water with a dehumidifier is minimal over several weeks. To dry out a boat which is wet (laminate) takes months, with heat and low humidity. Foam is more porris than laminate, but the moisture on the surface will come out fairly rapidly--that deep in the foam, will take a long time. Once foam has moisture in it, probably the best way to resolve the problem is to replace the foam. But in your case, you don't know for sure if there is water in the foam. Certainly not hurt to use the dehumidifier--but doubt it will solve the problem/
 
First, I really doubt anyone with a Mako 236 INBOARD is running at 37 knots (10 more than yours). Second, you need to weight it. It should be about 3800lbs dry. If it does have a lot of water in it, I would start looking for plugged drains in the stringers or encapsulated areas. Third, no, you shouldn't run a dehumidifier in your bilge. Household dehumidifiers are not marine safe. You would be better off shrink-wrapping the boat and vacuum out any remaining bilge water. Have vents put in the shrink-wrapping and open all doors and prop open floor hatches. The boat will dry out well in a few weeks.
 
quote:
Originally posted by Stephen

First, I really doubt anyone with a Mako 236 INBOARD is running at 37 knots (10 more than yours). Second, you need to weight it. It should be about 3800lbs dry. If it does have a lot of water in it, I would start looking for plugged drains in the stringers or encapsulated areas. Third, no, you shouldn't run a dehumidifier in your bilge. Household dehumidifiers are not marine safe. You would be better off shrink-wrapping the boat and vacuum out any remaining bilge water. Have vents put in the shrink-wrapping and open all doors and prop open floor hatches. The boat will dry out well in a few weeks.

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They do make marine grade dehumidifiers, and they work well. I have seen many that sit over the galley sink when in use. Google is your friend here. I had one for years that was stainless. But curious why are household humidifiers not marine safe? They are grounded. How about coffee pots, microwave ovens, and toasters. I have never written up a boat for having any one of those, nor a humidifier. I did nail a hair dryer one time, the cord was extended with a taped joint. It was done to allow the hair dryer to be plugged into the V berth plug, as the GFI plug was bad in the head. If my boat was wet it would get a dehumidifier, after I checked lumbers etc..Fred
 
quote:
Originally posted by delan

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Is it possible that your friends are confusing knots with mph. An old PowerBoat guide lists this boat as 35mph max. Thats 30.4 knots. Remember that manufacturers also rate them with 1 80 pound person (jockey) on-board and 1 gallon of gas, and perfect water conditions. in the 70's and now they want max speed for advertising purpose. I would have absolutely no concern about this speed in a sea trial, assuming everything else appeared normal. BTW are all of your 236 friends the same year as yours? If not things change, They could have found they could get an extra 3 knots by changing the shaft angle by 2 degrees and done this in later years, Also I find that boat owner in general lie about speed, as in your boat is slower than mine... Fred
 
It's not the grounding. Household dehumidifyers would not have a marine-safe fan motor. regular motors spark, and if in the bilge, can cause the same explosion hazzard as a non-marine grade alternator.
 
quote:
Originally posted by fmoor

quote:
Originally posted by delan

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Is it possible that your friends are confusing knots with mph. An old PowerBoat guide lists this boat as 35mph max. Thats 30.4 knots. Remember that manufacturers also rate them with 1 80 pound person (jockey) on-board and 1 gallon of gas, and perfect water conditions. in the 70's and now they want max speed for advertising purpose. I would have absolutely no concern about this speed in a sea trial, assuming everything else appeared normal. BTW are all of your 236 friends the same year as yours? If not things change, They could have found they could get an extra 3 knots by changing the shaft angle by 2 degrees and done this in later years, Also I find that boat owner in general lie about speed, as in your boat is slower than mine... Fred

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That makes the most sense Fred, the boat doesn't appear to ride low on the plane. I feel better already!
Thanks everyone for the replies.
Joe, Miami Beach.
 
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